THE NEMATOIDEA. 



545 



4. A cavity formed by invagination of the ectcderm 

 (epicoele). 



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- 

 form spines or papillae, "in DesmoscoUx, the papillae and setoa 

 acquire an almost Annelidan aspect, and the annulation of 

 the body is much more distinct than in any other Nematoid 

 Worm. 



a, 



Fig. 15^.— Angiiilliila brsvispinun. (After Clans.) * 



I. Male. II. Female. III. Female genital organs. IV. Seminal corpuscles in dif- 

 ferent stages of development. 



cesophasru^ ; a', chitiiuzed oral capsule ; c, gastric, and d. rectal, portion of the 

 alimentary canal, yl, anns ; gg\ anterior and posterior thickenings with their 

 commissures ; G, sexual apnr'tuie ; F, fatty-looking inland ; r, dilatation of the 

 litems, serving as a recoptarnlum seminis ; Z>, nnicclliilar cutaneous glands at the 

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

 ov, ovarium ; T^, testis ; S, seminal corpuscles. 



^ " Ueber einige in Humus lebende Anguillulluen." (ZeUschri/t fur wiss. 

 Zoologie^ xii.) 



