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states that in the young the tige has its apex with the rings half marked. 

 From the character of the figure it is apparent the drawing was made 

 firom a dead specimen, probably a dried one, in which, owing to the 

 contraction of the tissues, circular cracks had taken place, a fact which 

 any microscopist who examines the antennae of many of the Cloportides 

 under the glass must be fully aware of. The specimen also which he 

 figures as the yoimg of Scyphax, judging from its tail appendage, can 

 scarcely belong to that genus at all ; at least, though I have carefully 

 examined the young of all our native genera, most of them recently 

 hatched, yet I never met an instance in which the tail appendages dif- 

 fered much from that of the full-grown animal : but we will speak of 

 this anon in our enumeration of genera. 



There is one objection which has been started to using the characters 

 of the tige as generic, which must be noticed, i. e. that in the young the 

 number of joints are less than in the adult This statement is only 

 partially true. For instance, in most of the genera in which the antennae 

 are multi -articulate, the antennse of the young and adult differ much; 

 but in those of the second and third types, given above, in some species 

 there is no difference at all, the articulations being all present, though 

 the terminal ones are much shorter than normal. This is the case, for 

 instance, in very young P.pruinosus and P. scaler j even when the coxae 

 of the seventh cephalo-thoracic segments and the legs of the same pair 

 are absent : and even where it holds good there can be no mistake, for 

 other characters, such, for instance, as that noted above, the absence 

 of the seventh coxae, at once marks the animal as immature ; hence I 

 think Dana is wrong in making sub-genera of Trichoniscus, Porcellio, 

 and Oniscus, merely because the number of joints in their antennae have 

 been too much dwelt on. 



IV. — Form and relations of the last abdominal ring and its appendages. 

 Although the characters of these latter have been long employed in 

 diagnosis, yet it would appear that their true homological value has 

 neither been appreciated nor imderstood : for, although in aU the genera 

 of this group their presence has been recognised under the names of 

 *^ abdominal false feet j*^ ^^ caudal appendages," and ^^ appendages of the 

 last segment^" yet, as far as I am aware, the ti*ue relations subsisting be- 

 tween them and the so-called *' thoracic" feet have been either over- 

 looked or only hinted at. 



Their structure in all the genera is pretty much the same : a broad 

 basal joint, articulated somewhere at the termination of the last abdo- 

 minal ring, and furnished (except, perhaps, in Tjlos, which I have 

 never seen) with a pair of dissimilar appendages, the external generally 

 broad, the internal pointed and linear, and inserted above the external ; 

 or, to speak more correctly, an appendage of two or more articulated 

 joints, the basal joint furnished at its inner side with an accessory ap- 

 [penda^; that is, a foot, in which the second (the first being the poste- 

 rior angle of the ring), third, and fourth, &c., articulations are present, 

 the second, or ischium, being furnished with an appendage. 



