CRUSTACEA. 133 



diately following, statement, that " dans le honiard ies 



" pedicnlcs oculaires se developpent plus tot et indiquent plus claire- 

 " ment que cliez les Mysis leur communaute d'origine avec les 

 " organes appendiculaires." It appears, therefore, as is indeed 

 directly stated in p. 29, that in spite of some confusion of expression 

 in p. 62, Professor Van Beneden does, in fact, consider the ocular 

 pedicule as the appendage of the anterior segment. He also regards 

 the " telson" as representing a posterior segment, and adopts, there- 

 fore, Milne Edwards' view, that the body of a Crustacean consists of 

 twenty-one segments, in opposition to those naturalists who see only 

 twenty. 



So accustomed are we to see the organs of sensation located in 

 the head that we cannot but feel astonished to find that the ear of 

 Mysis is not in its head, but in its tail. This curious fact, which 

 was discovered by Leuckart, has been confirmed by several distin- 

 guished naturalists, and last, not least, by M. Van Beneden, who 

 moreover, like Kroyer, has traced a nerve from the last ganglion to 

 the otolithe. We may find a parallel case in the little worm described 

 by Quatrefages, under the name of Polyojihthalmus, which has eyes 

 on every segment of the body. Amphicora Sahella also, another 

 ■worm, has, according to O. Schmidt, eyes in its tail. Moreover, 

 among insects, the Crickets and Grrasshoppers have an organ in the 

 anterior pair of legs, which is considered by some good observers to 

 be an ear, but which certainly is, like the remarkable organ at the 

 base of the halteres of Flies, an organ of some special sense, 

 though what that sense may be it is not so easy to decide. 



The Professor does not always do justice to his predecessors. 

 Thus under the Cetoehilidae he refers only to Roussel de A^auzeme 

 and Groodsir, entirely ignoring all that has since been written on this 

 family. He mentions only one species belonging to the group, and 

 this one he attempts to identify with the Cetochilus septentrionalis. 

 His description of it, however, clearly shows that it does not belong 

 to this family of Entomostraca at all, but is one of the Calanidse, 

 and belongs probably to the genus Calaniis, which may at once be 

 distinguished from Cetochilus by the position of the eyes. Many of 

 the Calanoidea have at the anterior extremity of the cephalothorax 

 two curious horns, which were mistaken by Groodsir for anteimse. 

 Professor Van Beneden corrects this error, which, however, was 

 pointed out long ago by Baird, and has been adopted by no subse- 

 quent writer. The description which he gives of the difierent parts 

 is almost useless for identification, as the characters mentioned are 

 those which are common to many species: take away the extremities 

 of the antennae (antennules of V. Beneden), those of the abdomen, 

 and the posterior pair of legs ; half the species of Calanus would be 

 undistinguishable from one another. Of this our author was e\'i- 

 dently not aware, and his attention has not been particularly draT\Ti 

 to the characteristic organs. Moreover, we cannot supply the de- 

 ficiencies from the plate. He gives thi'ee very dissimilar represen- 

 tations of the antennae ; two of them, however, are small, and perhaps, 



