Tin; 



4. A cavity formed by invagination of the ectoderm 

 (epicoele). 



And whether any given perivisceral cavity belongs to one 

 or other of these types can only be determined by working 

 out its development. 



Tin; NEMATOIDEA. The " Thread-worms " have elongated, 

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

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

 limbs, though they may occasionally be provided with seti- 

 f orm spines or papillae. In Desmoscolex, the papillae and setae 

 acquire an almost Annelidan aspect, and the annulation of 

 the body is much more distinct than in any other Nematoid 

 Worm. 



PIG. 155.Anyuillula breviapinus. (After Claue.) 



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

 ti'ivnt stages of development 



a, oesophagutf ; ', clutiuized oral capsnle ; c, gastric, and d. rectal, portion of the 

 alimentary canal. A, anus; gg r , anterior and posterior thickenin"s with their 

 commissures ; <?, sexual aperture ; F, fatty-looking inland ; r, dil.-it.-ition of the 

 uterus, serving as a reccptaculum seminis ; I), unicellular cutaneous glands at the 

 anal extremity : jy, glandular mass, \\uli its excretory duct above the gizzard ; 

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



1 " Ueber einige in Humus lebende Anguillulinen." (Zetechrift fnr wist. 

 Zoologie, xii.) 



