206 



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 



tr. 

 FIG. 126. 



A, exopodite of first pleopod of Porcellio scaber ; the tuft of pseudo-tracheae is seen through 

 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 ; n, nucleus of hypodermis of pseudo-tracheal tube; o, external open- 

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



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

 mentioned the pleopod s 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- 

 m posed of two segments, of which 

 the proximal corresponds to the 

 main part of the endopodite 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 



Second pleopod of an oyigerous female Unsegmented. 



of Nerocila maculata, showing persistence J n the Asellota the SBXUal Hiodi- 

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



podite ; ex, exopodite ; e, laminar expan- nCatlOnS OI the pleopods are more 



sion from outer edge of protopodite. i jj'/rr ii. rn 



complex and diner 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, 



ex. 



FIG. 127. 



