250 ELEMENTARY BIOLOGY. [CHAP. 



y. The dorsal or peritoneal pores ; small median per- 

 forations of the body-wall, lying at the bases of 

 the somitic constrictions between all but some 

 few of the anterior segments. They are best 

 seen in specimens which have been preserved 

 in spirit. If examined in freshly killed worms, 

 their presence can be made manifest by gently 

 squeezing the body, whereupon there will exude 

 from each a drop of perivisceral fluid. 



S. The sexual apertures. Examine the worm from 

 beneath, and note the presence of two glandular 

 enlargements immediately external to the ventral 

 setse of the 1 5th segment. Each surrounds the 

 slit-like orifice of the vas deferens of its own side. 

 Opening, in a line with the above, on to the 

 surface of the 14th segment, there are the smaller 

 apertures of the oviducts. 



The ventral integument of segments 9 to 11 

 (more rarely 8 to 12^ is generally swollen, like 

 that of the lip of the vas deferens or the clitellum, 

 owing to the presence of the albumeniferous 

 (so-called capsulogenous) glands. (Cf. p. 247.) 



The exact function of these is at present un- 

 known. 



Examine the somitic constrictions in this 

 region from the side. There will be found, 

 opening upon those which subdivide segments 

 9 — 10 and 10 — 1 1 in a line with the lateral setae, 

 the small apertures of the spermathecm. 



Not unfrequently one or other of these may 

 open by two orifices, and their presence may 

 easily be demonstrated by gently squeezing the 

 body. 



