NEPHRIDIA. CRURAL GLANDS. 



563 



is removed from the body, and consequently is not shown in 

 Fig. 342. This internal vesicle was discovered by Sedgwick 

 and is known as the end-sac. Its discovery was of consider- 

 able morphological importance not only because it cleared up 

 the question of the arthropod body-cavity, but also because 

 it threw considerable light upon the general theory of the 

 coelom. 



The fourth and fifth pairs are very considerably larger than 

 those behind, and are in other respects peculiar. The great 

 mass of each organ is placed behind the leg on which the external 

 opening is placed, immediately outside one of the lateral nerve- 

 cords. The external opening, instead of being placed near the 

 base of the leg, is placed 

 on the ventral side of or 

 in close relation with the 

 proximal spiniferous pad. 

 It leads into a portion 

 which clearly c o r r e - 

 sponds with the collect- 

 ing vesicle of the hinder 

 nephridia. This part is 

 not, however, dilated into 

 a vesicle. The three pairs 

 of nephridia in the three 

 foremost pairs of legs are 

 rudimentary, consisting 

 solely of a vesicle and 

 duct. The salivary glands are the modified nephridia of the seg- 

 ment of the oral papillae. 



The crural glands are seen at their simplest in P. capensis, in 

 which they are present in both sexes and in all the legs except 

 the first. They open externally to the nephridia (except in 

 legs 4 and 5) and consist of a glandular vesicular body contained 

 in the pedal compartment of the body cavity and communicating 

 with the exterior by a narrow duct. They are absent in P. 

 novae-zealandiae and novae-britanniae. As a rule they are only 

 present in the male. There may be two pairs of them in each 

 leg and their opening is often placed on a prominent papilla (many 

 legs of the neotropical species, last leg in male of Cape species, 

 Fig. 336), 



FIG. 342. -Xephridium from the 9th pair of legs of 

 P. capensis. o.s External opening of segmental 

 organ ; p.1 internal opening of nephridium into 

 the body cavity (lateral compartment) : s vesicle 

 of segmental organ : s.c.l, s.c.2, s.c.3, s.cA succes- 

 sive regions of coiled portion of nephridium ; s.o.t. 

 third portion of nephridium broken off at p.f from 

 the internal vesicle, which is not shown (after 

 Balfour). 



