THE NEMATOIDEA. 



545 



the ectoderm 



4. A cavity formed by invagination of 

 (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 papilla?. In Desmoscolex, the papilla? and seta? 

 acquire an almost Annelidan aspect, and the annulation of 

 the body is much more distinct than in any other Nematoid 

 Worm. 



Fig. 155.— AnguUlula brevispinus. (After Clans.) 1 

 I. Male. II. Female. III. Female genital organs, 

 ferent stages of development. 



IV. Seminal corpuscles in dif- 



a, cesophagu-s ; a' , chitiaized oral capsule ; 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 gland ; r, dilatation of the 

 uterus, serving as a receptaculum seminis ; Z>, unicellular cutaneous glands at the 

 anal extremity ; Z> / , glandular mass, with its excretory duct above the gizzard ; 

 ov, ovarium ; Z*', testis ; S, seminal corpuscles. 



1 " Ueber einige in Humus lebendc Anguillulinen." (Zeitschrift fur wiss. 

 Zoologie, xii.) 



