THE BRITISH WOODLICE. 



45 



Cerzbxtl ganglia 



(b) Masses of cellules in the head, very greatly developed in 

 Ligia oceanica (but numbering scarcely more than ten in Oniscus 



asellus), which have no external 

 opening. They also function as 

 excretory organs (5, p. 263), and 

 have been called " cephalic nephro- 

 cytes." 



(c) Other " branchial nephro- 



cytes " are situated on the dorsal 



surface between the last thoracic and 



^Z31fGf a t ^ le ^ rst abdominal segments, as well 



==J^tIL J—J?- > as between those that follow, with 



the exception of the last two ; they 

 are in distinct patches, one on each 

 of the middle line in Ligia, but more 



Cm7l7TUSSUr£S 



surrounding 



~?/w gul/et 



and uniting 



Ti? form 



a 



double cord 



7/ie 

 alanen&az/ 

 canal. 



T/w facte segmerifo 

 OVARIES. 



FIG. 19. — THE NERVOUS SYSTEM. 



(Oniscus asellus.) 



or less continuous in 

 Oniscus (5, p. 265). 



(d) The digestive 

 glands have also been 

 shown to be excretory 

 (5, P- 270). 



Nervous system. — 

 The nervous system con- 

 sists of paired ganglia in 

 the head, above the 

 alimentary canal which 

 send off nerves (commis- 

 sures) that meet below, to 

 form a double nerve cord 



-FEMALE REPRODUCTORY ORGANS. 



(Oniscus asellus.) 



with ganglia at intervals 

 (see fig. 19). 

 Reproductive organs. 



— In the female there are 



a pair of ovaries in the positions shewn in fig. 20 ; and ducts run 



to the underside of the fifth thoracic segment. 



