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 pubUshed 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 unpubUshed data, give at best an imperfect survey of the 

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

 also confessedly artificial and incomplete. 



KEY TO NORTH AMERICAN ACANTHOCEPHALA 



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



Family NEOECHiNORHYNCHmAK Ward . 



Primitive Acanthocephala with hypoderm consisting of a syncytium in which arc six giajil 

 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 maf s. 

 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 1005 . . 3 



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

 center and basal rows. Cement gland with eight nuclei. 



3 (4) Twelve hooks in each circle. 



Neoechinorhynchus gracilisentis (Van Cleave) IQI.^ 



Body small, tapering slightly toward both ends, bent 

 into a crescent. Mature females 1.7 to 4 mm. lonff: 

 maximum width 0..5S mm. just anterior to centi-r of 

 body. Males 1.5 to ,^ mm. long, ma.xinuim l)rcadth o.j 

 mm. Proboscis slightly longer than wide w^ilh con- 

 striction between second and third row of hooks. 

 Hooks delicate, in anterior rt)W curved 15 ui 17^ 

 long, in middle row 1 2 to 1 5 M long, m basal row nearly 

 straight, 15 to 20/i lonK- Knibryos spmdlo shaped. 36 

 to 40 M long by 10 m broad . . ,„• • u- 



. . In intestine and ceca of hickory shad; llUnois Kirer. 

 Fig. 845. Neoechinorhynchus gracilisentis. n^fr^Kf^r tr^ \Ttv 

 Proboscis. X9S; hooks and embryos, X OctoDer lo iua\ . 

 310. (After Van Cleave.) 



4 (3) Six hooks in each circle. 



