PARASITIC ROUNDWORMS 545 



pig finds its intermediate host in terrestrial beetle larvae. Of 

 forms from aquatic hosts it is inferred that the ripe embryos dis- 

 charged into the water with the feces of the host attain by chance 

 a suitable intermediate host which is probably a crustacean or in- 

 sect and in that develop to the end of the larval stage. When 

 this intermediate host is eaten by the final host the parasite reaches 

 the place in which it can complete its development. 



Almost no records have been published of Acanthocephala from 

 North American fresh-water hosts. My own collections and re- 

 cent papers by Van Cleave, to whom I am indebted also for valu- 

 able unpublished data, give at best an imperfect survey of the 

 field. The system used, which follows in the main Lube's work, is 

 also confessedly artificial and incomplete. 



KEY TO NORTH AMERICAN ACANTHOCEPHALA 



1 (10) In hypoderm and lemnisci only a few giant nuclei. 



Family NEOECHINORHYNCHIDAE Ward . . 2 



Primitive Acanthocephala with hypoderm consisting of a syncytium in which are six giant 

 nuclei, ordinarily arranged so that five lie in the mid-dorsal line and one in the mid-ventral. 

 One lemniscus contains two giant nuclei and the other only one. These nuclei are usually 

 conspicuous on external examination. 



Proboscis sheath contains only a single layer of muscles. Cement gland a compact mars. 

 Neck lacking. Muscles weakly developed. Lacunar system with simple circular connec 

 tions. . . 



2 (9) Proboscis globose, or nearly so; with three circles of hooks. 



Neoechinorhynchus Stiles and Hassall 1905 . . 3 



Proboscis short, globose, with few hooks. Hooks of anterior row much larger than those Li 

 center and basal rows. Cement gland with eight nuclei. 



3 (4) Twelve hooks in each circle. 



Neoechinorhynchus gracilisentis (Van Cleave) 1913. 



Body small, tapering slightly toward both ends, bent 

 into a crescent. Mature females 1.7 to 4 mm. long; 

 maximum width 0.38 mm. just anterior to center of 

 body. Males 1.5 to 3 mm. long, maximum breadth 0.3 

 mm. Proboscis slightly longer than wide with con- 

 striction between second and third row of hooks. 

 Hooks delicate, in anterior row curved, 15 to 17/1 

 long, in middle row 1 2 to 1 5 n long, in basal row nearly 

 straight, 15 to 20 ju long. Embryos spindle-shaped, 36 

 to 40 ju long by 10 /x broad. 

 FIG. 845- Neoechinorhynchus gracilisentis. In intestine and ceca of hickory shad^ Illinois River; 



Proboscis, X95J hooks and embryos, X October to May. 



310. (After Van Cleave.) 



4 (3) Six hooks in each circle 5 



