NEMATOMORPHA. 293 



The sexes are separate, and the generative organs are paired ; they 

 open to the exterior, with the anus near the hind end of the body. 

 The ovaries are metamerically repeated masses of cells on each side. 

 The ova are collected into two tubes the egg-sacs, which behind 

 become the oviducts. The oviducts open into a median atrium, 

 which also receives the opening of the single receptaculum seminis. 

 The male organs are much the same, 

 except that the two vasa deferentia 

 open separately into the rectum 

 (cloaca). The male caudal region is 

 forked, and is devoid of spicula. 



In the adult stage these animals are 

 free and sexually mature, but the 



-,. , FIG. 238. Larvae of Gordius subbi- 



alimentary canal is generally degen- furcm (after Me issner). a, in the 



erate, being occluded in front, and egg-membrane with protruded pro- 



, , , , boscis; 6, out of the egg-membrane; 



presumably functionless. They are c> with invaginated proboscis, 

 found in fresh -water ponds and 



streams, and move in an undulating manner. The eggs give rise 

 in the water to an embryo, with a circle of boring-spines, which 

 leaves the egg and migrates into insect larvae (Ephemerid larvae, 

 etc., they have been found even in fishes, molluscs, and oligochaetes) 

 and there encysts. Water beetles and other aquatic predatory insects 

 eat with the flesh of their prey the encysted young forms, which 

 then develop in the body-cavity of their new and larger host to 

 young Gordiidae, which make their way into the water. Gordius L. ; 

 Nectonema Verr., a marine form, life-history unknown. 



Class III. ACANTHOCEPHALA.* 



Elongated round ivorms, with protrusible proboscis furnished with 

 hooks ; without mouth, and alimentary canal ; icith a body-cavity, into 

 which the ova are dehisced and the oviducts open ; parasitic. 



The saccular, often transversely wrinkled body begins with a 

 proboscis, which is furnished with recurved hooks, and can be 

 retracted into a tube projecting into the body-cavity (sheath of the 



* Besides Dujardin, Diesing, 1. c., compare: R. Leuckart, " Parasiten des 

 Menschen," torn 2, 1876. Greeff, " Untersuchungen liber Echinorhynchus 

 miliaris," Arch, fur Naturgesch, 1864. A. Schneider, "Ueber den Bau der 

 Acanthocephalen," Mutter's Archiv., 1868. Also the Sitzungsbcrichte der 

 Oberhessischen Gesellschaft fur Natur- und fleilkunde, 1871. B. Grassi and S. 

 Calandmccio, " Ueb. einen Echinorhynchus, welcher auch in Menschen parasitirt 

 u. dessen Zwischemvirth ein Blaps ist," Centralbl. fur Bakt. u. Parasitekund. 

 3, 1888. 0. Hamann, Die Nemathelminthen, Heft 1, Monographic der Acantho- 

 cephalen, Jena 1891 ; Heft 2, 1895. 



