THE NEMATOIDEA. 



545 



4. A cavity formed by invagination of tlie ectoderm 

 (epiccele). 



And whether any given perivisceral cavity belongs to one 

 or other of these types can only be determined by working 



out its development. 



The Nematoidea. — The "Thread-worms" have elongated, 

 rounded bodies, which usually taper toward one or both ends; 

 they are not divided into segments, and they are devoid of 

 limbs, though they may occasionally be provided with seti- 

 f orm spines or papillae. In Desrnoscolex^ the papillae and setse 

 acquire an almost Annelidan aspect, and the annulation of 

 the body is much more distinct than in any other Nematoid 

 Worm. 



Fig. loo.—Angulllula brevispinus. (After Clans.) i 



I. Male. II. Female. III. Female gt-nital organs. IV. Seminal coi-pusclcs in dif- 

 ferent stages of development. 



a, oesophagus ; a', chitinized oral capsnle ; c, gastric, and d, rectal, portion of the 

 alimentary canal. A, anus; gg', anterior and posterior thickenings with their 

 commissures ; G, sexual aperture ; F, fatty-looking irland ; r, dilatation of the 

 uterus, serving as a receptacniura seminis ; D, nricelhilar cutaneous glands at the 

 anal extremity ; Z>^ glandular mass, wiih its excretory duct above the gizzard ; 

 ov, ovarium ; 7>, testis ; S, seminal corpuscles. 



» " TJeher einige in Humus lebende Anguillulincn." {ZeUschrift fur win. 

 Zoologicy xii.) 



