2o6 



THE CRUSTACEA 



edge and grooved for the reception of the bundles of spermatozoa 

 which it is its function to transfer to the female. This rod appears 



Cr. 



Fig. 126. 



A, exopodite of first pleopod of Porcdllo scaber ; the tuft of pseuilo-traclieae is seen tlirougli 

 the transparent cuticle. B, vertical transverse section through same. C, part of section further 

 enlarged, art, point of articulation of exopodite with peduncle ; c, cuticle ; gr, " grooved area " 

 of cuticle ; hy, hypodermis ; ii, nucleus of hypodermis of pseudo-tracheal tube ; o, external open- 

 ing of pseudo-tracheae ; tr, pseudo-tracheae. (After StoUer.) 



to be the distal segment of the endopodite. In the groups just 

 mentioned the pleopods of the first pair are similar or present 



but slight differences in the two 

 sexes, but in the majority of the 

 Oniscoidea and in the Asellota the 

 first pair are also modified in the 

 male sex. In the males of the 

 Oniscoidea the inner ramus of the 

 second pair is styliform and com- 

 posed of two segments, of which 

 the proximal corresponds to the 

 main part of the endojDodite in 

 groups above mentioned. In the 

 family Ligiidae this is the only 

 modification of the pleopods in the 

 male sex, but in all the other 

 Oniscoidea the first pair have the 

 endopodites also styliform, though 

 unsegmented. 



In the Asellota the sexual modi- 

 fications of the pleopods are more 

 complex and difter from those of all 

 other Isopoda. The second pair are always absent in the female. 

 In the females of Asellidae the first pair are small, uniramous, and 

 separate ; in the Stenetriidae and Parasellidae they are coalesced, 



Fig. 127. 

 Second pleopod of an ovigerous female 

 of Nerocila maculata, showing persistence 

 of the appendix masculina (m). en, endo- 

 podite ; ex, exopodite ; c, laminar expan- 

 sion from outer edge of protopodite. 



