unclean animals are employed to symbolize evil and unclean spirits as well as men, as the serpent, the dragon, or crocodile,1 the lion, and the scorpion.3 By way of corollary to the present short chapter, I shall devote a few pages to a very interesting subject, intimately connected with the animals whose history and habits I have just described, and which marks out the plan upon which the wisdom, power, and goodness of the Creator have been manifested in animal structures. I allude to what has been named the conversion of organs, by which term is meant, not only in particular instances, multiplying the functions of any given organ, as, for instance, when the tail of an animal is employed like a hand, to take hold of the branch of a tree, and to assist in locomotion, as in the chameleon, and certain monkeys; and the tongue is also made to subserve to prehension, as in the case of the giraffe; but likewise when the organ is converted from one use to another, as when the anterior leg is taken from locomotion, and given to prehension, as the human hand; or as when all the ordinary organs of locomotion in one tribe are in another converted into oral organs, either to assist in mastication, or to discharge the office of a lip, as in the Crustaceans and Centipedes. In the investigation of this curious and interesting subject, the class of Myriapods affords an example, if I may so speak, of the gradual conversion of locomotive organs into auxiliary oral ones. Something of this kind I have before stated, is discoverable in certain Annelidans, either related to those animals or their analogues. In the Introduction to Entomology it is observed, with respect to the larves of many Hexapod Condylopes, that their progress, towards what is called their perfect state, is by losing their spu rious legs or prolegs, and by acquiring organs of flight; whereas in the Myriapods, the reverse of this takes place; instead of losing legs and shortening their body, some of them, when first hatched, have only six legs, representing the six legs of Hexapods, and all in their progress to their adult state acquire a large number of what may be denominated spurious legs, which support many additional segments. As the Chilognathans, in their young state, come nearest to the insect or hexapod tribes, I shall begin by stating the changes they undergo. In the most common species," according to De Geer's description and figure, the animal is divided into 1 Revel. xx. 2. 4 Ateles. 6 Julus terrestris. 2 1 Pet. v. 8. 3 Luke, x. 19. three principal parts, as in Hexapods; first, there is a head with antennæ, and the usual oral organs, though a little aberrant in their structure; next, there is a trunk, consisting of three segments, each bearing a pair of legs; and lastly, there is an abdomen, divided into five segments, without legs.1 With regard to their oral organs, they correspond with those of Hexapods, both in number and kind, for in the mouth, above is a representative of the upper-lip; below this is a pair of mandibles or upper-jaws; next follows a lower-lip, consisting of three pieces united together, the two lateral ones analogous both to the lower-jaws of Hexapods, and the first pair of maxillæ of Crustaceans; and the intermediate one, resolvable into two pieces, representing the lip of the former and the second pair of maxillæ, according to Savigny, of the latter, from his figures,* the maxillary and labial feelers appear to have their representatives; yet though he has figured he does not notice them as feelers." The six original or natural legs of the Iulus are its first. organs of locomotion, which when the animal is arrived at its complete development, as to number of legs and segments,are said still to maintain their original function, although probably diminished in energy; the two first pairs are, however, as it were, applied to the mouth, the segments that bear them being very short. The sciatic joint or hip of the first pair forms a single piece; those of the second are also united and more elevated; but those of the third are distinct: so that in this Order of the Myriapods we see the first tendency towards employing what in Hexapods wear the form and perform the functions of legs as auxiliaries of the mouth, and of the locomotive function being devolved upon organs which have no representative in Hexapods, except in their incipient state. To proceed next to the Chilopodans-it has not yet been ascertained what changes they undergo in the progress of their growth, save that the number of legs and segments increases till they have arrived at their full size, nor is it known how many they have when first hatched, but, from their structure, it seems evident that the analogues of the two first pair of legs of the Chilognathans, can never be employed in locomotion; and further, that not only is their first or hip-joint united with 1 De Geer, vii. 583. t. xxxvi. f. 20, 21. 2 Anim, sans Vertebr. Mem. ii. t. f. 1. o. 2. o. 3 He says that the pieces forming the labium are Denuces des palpes. Ibid. p. 44. 4 Coxa. 5 De Geer, vii. 562. its fellow, so as to form a kind of auxiliary lip, but the other articulations are converted into prehensory organs, instead of a locomotive one, in the first pair armed at the end with a minute forceps, and in the second with a fang resembling the tooth of a serpent, having a pore at the extremity for the emission of poison, connected with an Ioterium or poison bag. Here then, in these two orders of the Myriapods, we have a regular conversion of organs: those that in the Millipedes are used for locomotion, in the Centipedes, exchange that function for that of prehension, both agreeing in being auxiliary, at their base, to mastication, but the latter with a greater momentum. The reason of this change in the functions of these organs we shall readily see when we consider the habits and food of these respective Orders. The Chilognathans deriving in general their nutriment from putrescent substances whether animal or vegetable, have no resistance to overcome, and therefore require not the aid of additional prehensory organs to enable them to execute their offices; while the Chilopodans, having to contend with living animals, must put them hors de combat, either by killing them, or deadening their efforts, before they can devour them. In this last Order we find that though the two first pairs of legs have a new office, the third pair are still used for locomotion. From the oral organs and their auxiliaries of the Myriapods to those of the Crustaceans, the interval is not very wide; and amongst the latter the Isopods, especially the terrestrial ones, as might be expected, approach the nearest to them. De Geer observes that the common wood-louse,1 which in its adult state has fourteen legs; when it first leaves the egg, has only six pairs and six segments; thus doubling the number of the Hexapods and Julus; and in this animal and its relation Ligia, the thoracic legs are all used in locomotion; but when we examine the aquatic, especially marine, genera of this Order, as Idotea, Stenosoma, &c., we find that the first pair of thoracic legs is taken from that function, and made auxiliary to the organs of the mouth. Leaving the Isopods, if we go to the Decapods, amongst those with a long tail, which from their cylindrical form and other circumstances, are nearer to the Chilognathan Myriapods than to the Chilopodan, taking the lobster, for our type, we find the organs analogous to the six legs of Hexapods, exhibiting a new character: for from the outer side of their basal joint issues 1 Oniscus Asellus. 2 vii. 551. 3 Macrouri an organ which is peculiar to these legs. The organ I allude to is called, by M. Savigny, a flagrum or whip; and, by M. Latreille, a flagelliform palpus or feeler; it usually consists of two parts, an elongated exarticulate base, representing the handle of the whip; and an annulated or jointed part generally forming an angle with it, representing the lash: the mandibles also have feelers of the usual structure. The organs above alluded to, show that all the representatives of the legs of Hexapods in the lobster, are converted to a new functionwhether precisely analogous to that of feelers is not clear. In the lobster the basil joints of the first pair of maxillary legs are dilated, and the whole organ may be regarded as maxilliform; but in the second it is palpiform, and in the third it resumes the joints and appearance of a crustaceous leg, and is densely ciliated, which seems to indicate that it is used in swimming. In the common crab,1 amongst the short-tail Decapods,' the legs in question seem all taken from locomotion, and the second pair does not differ from those of the lobster; but the last, though consisting of the same number of joints, is very different, the two intermediate joints being dilated, and the two legs together forming as it were a pair of folding doors, which close the mouth externally, the three last joints resembling those of the legs. These animals, therefore, in some sort, the flatness of their body and this double auxiliary lip considered, present the same analogy to the Chilopodan Myriapods, that the lobster does to the Chilognathan. In both we see, by their feelers, there is a further conversion of these organs into instruments connected with the mouth; so as to bring them nearer to the nature and use of maxillæ or under jaws, and of a labium or under-lip. It appears from the experiments and observations of Rathke that the long-tailed Decapod Crustaceans do not change the form, or increase the number of locomotive organs, that distinguish them when they issue from the egg. Once residing a few weeks on the northern coast of Norfolk, where the sea, at low water, retires to a considerable distance from the high water mark, I had an opportunity of witnessing the proceedings of a species of crab very common there, and varying greatly in 1 Cancer Pagurus. 2 Brachyuri. 3 Récherches sur le dévélopement des Ecrevisses. Abstract of Ann. des Sc. Nat. xix. 442. 4 Ibid. 463. 5 Cancer Manas. L. Mr. Westwood, in a letter received since this went to press, expresses his conviction that Crustaceans do not undergo any meta. morphosis. Besides a variety of other arguments which he will himself bring size, some, if my memory does not deceive me, scarcely exceeding the size of a pea, others being three or four inches in diameter, and all exactly corresponding in every particular; so that it seems probable that the short-tailed tribe also undergo no change, except of size, though, as we have seen above the terrestrial Isopods acquire additional legs in their progress to maturity. The legs, however, of these Crustaceans cannot be regarded as analogues of the legs of Hexapods, but rather of the acquired legs of the Myriapods. In order to form a clear notion of the object of Providence in thus, as it were, taking certain organs from locomotion, and forming a new set for that purpose, and multiplying those connected with the seizing and mastication of the food of the animals in which this metamorphosis takes place, it would be necessary to watch their proceedings in their native element, the water, to ascertain the nature of their food, their mode of taking it, and other circumstances connected with its conversion into a pulp proper for digestion; but as few can have an opportunity of doing this, we can only conjecture that this multiplicity of organs is rendered necessary by the circumstances in which they are placed, and the element they inhabit; for, as we have seen, no such conversion occurs in the terrestrial Crustaceans; probably the denser medium requires a more complex structure and more powerful action in the instruments connected with the nutriment of the animal. Having considered these instances of the legs of Hexapods being, as it were, metamorphosed into organs more especially connected with nutrition, I shall next mention, more briefly, some cases in which the oral organs themselves are modified to discharge other functions than what is usually their primary one. To begin with the Arachnidans or spiders. In these the twojointed mandibles or cheliceres, as Latreille calls them, are not organs of mastication solely; for though, from the vast strength and power of the first joint and its flat internal surface, we may conjecture that it assists in pressing the juices out of their prey, yet at the extremity of the second is a poison fang, being furnished, like the tooth of a viper or centipede, with a pore for emitting venom, which though not easily discovered in the smaller species, is visible under a lens in the larger; with these forward in due time, he lately met with young specimens of this crab at Conway, in N. Wales, only 1-16 of an inch in length, which did not differ from adult ones, |