( H ) 



That this is the true nature of the organ appears from the follow- 

 ing:— 



1st. The mode and point of articulation of the peduncle (basis) with 

 the last abdominal segment. 



2nd. The mode of articulation of the so-called external appendage 

 (ischium) and peduncle (basis). 



3rd. The difference in form and relation between the internal (ac- 

 cessory filament) and external (ischium) appendages. 



1st. The mode of articulation of the peduncle. 



By reference to the observations on the so-called '* epimerals and 

 posterior angles of the abdominal rings," it will be seen that, taking into 

 consideration the ultimate segment only, two principal types exist, viz., 

 those in which ** epimerals" or coxa) exist, as Ligia, and those in which 

 these organs are absent, as Oniscus, Porcellio, and, perhaps, Philoscia, 

 &c. 



Now, if we examine these, we will find that the point of articula- 

 tion between what we have called the peduncle, and the last abdominal 

 segment, is different in these two types. 



In the first (Ligia, for instance), it takes place at the posterior mar- 

 gin of the ring, in a notch fonned between what I have considered as 

 the coxoe and the posterior margin of the ring, by the whole superior 

 border of the peduncle, which is broad and flat, the exterior angle of 

 which forms a regular ball-and-socket joint, which is received into a 

 regular notch in the posterior angle of the ring, exactly similar to the 

 notch on the under side of the *' epimeraV of the cephalo-thoracic ring. 



In the other (Oniscus, to wit), the inferior portion of the peduncle is 

 narrowed, so that it appears to be articulated by the exterior angle only, 

 the interior border being produced into a lobe, and attached to the ex- 

 treme exterior edge of the last ring, or rather to a process of this ring, 

 visible only below, and which may be looked on as the coxa reduced to 

 a minimum and fixed to the ring ; the form of articulation is the same 

 as in Ligia. 



This view of relations receives further confirmation on examination 

 of the last abdominal ring in Philoscia and kindred forms, where the 

 articulation is completed externally by a small triangular lobe, differing 

 from the angle in Ligia only in size ; indeed, it is a question whether 

 I am strictly correct in describing Philoscia as wanting the **coxa" 

 in the sixth abdominal ring, and not as having the coxao fused to the 

 ring. 



The mode of articulation dependent on the development of coxae in 

 the last ring causes the peduncle to be more or less uncovered by the 

 preceding coxte, and has given rise to the erroneous description of 

 Brandt, already referred to, viz., ** Ligia) — Caudal appendages, one pair" 

 (Conspect, page 9); Oniscinae — " Caudal appendages, two pairs" (ib., page 

 12); the absence, or rather complete fusion, of the coxa with the last 

 ring causing the peduncle in Oniscus, &c., to be completely covered by the 

 coxae of the fifth rings, led Brandt to overlook its existence altogetlier, 

 and to mistake the terminal appendages for separate organs. 



