136 INVERTEBRATE ZOOLOGY 



tinue and pass on through the body cavity to an insertion on the 

 body wall as the retractors of the receptacle. 



A sheath passes backward from the posterior extremity of the 

 proboscis receptacle as the suspensory ligament which holds the 

 reproductive organs in place. The male organs consist of a pair 

 of testes and a group of cement glands which communicate with 

 the cirrus. The cirrus is contained within an evertible structure 

 at the posterior end of the body known as the copulatory bursa. 

 When protruded, this is a bell-shaped structure in the center of 

 which the cirrus is located. 



In the female, there is no persistent gonad. Egg masses are 

 formed very early and after fertilization these are broken up into 

 individual embryos each of which becomes surrounded by a 

 series of three embryonic membranes. The hard-shelled embryos 

 thus formed are usually ovoid or spindle-shaped in form. The 

 embryos are held for some time within the female's body cavity 

 which becomes filled with them. Finally, they are discharged 

 through an apparatus known as the selective apparatus (Fig. 

 71 B) which passes them down the uterus and out of the genital 

 pore. 



All classes of vertebrates harbor these parasites. Macracan- 

 thorhynchus hirudinaceus found in hogs is one of the most commonly 

 known species. The genera Echinorhynchus and Neoechinor- 

 hynchus are represented by several species in American fishes. 

 Several genera, including numerous species, infest the intestines 

 of birds and mammals. The genus Moniliformis occurs normally 

 in rodents but is also at least a facultative parasite of man. 



Outline of Classification 



Phylum Nemathelminthes, — Body covering a cuticula; wormlike; 

 unsegmented. 



I. Class Nematoda. — Complete digestive tract; lateral lines along 



sides of ])ody; body cavity a pseudococl. 



1. Order Trichosyringata. — Esophagus a small tul)e with cliitinous 

 lining. Trichindla, Triciwstrongylus. 



2. Order Myrosyringata. — Esophagus . prominent; muscular. 

 Ascaris, Heterodera, Rhabditis, Strongyloidcs, Syngamus, Ancy- 

 lostoma, Necator, Haemonchus, Filaria, Loa, Dioctophyvie. 



n. Class Gordiacea.^ — Body cavity lined with epithelium; no lateral 

 lines; larva in insects, adult in water. Gordius, Paragordius. 

 III. Class Acanthocephala. — Digestive organs lacking; always parasitic; 

 proboscis a hook-covered introvert. Echinorhynchus, Acanthocephalus, 

 Neocchinorhynchus, Gigantorhynchus, Macracanthorhynchus, Monili- 

 formis. 



