ACANTHOCEPHALA 



229 



of the neck is a pair of long- projections of the subcuticula called the 

 lemnisci, the function of which is not known. The excretory system con- 

 sists of a pair of nephridia which unite and open into the reproductive 

 duct. The nervous system consists of a central ganglion in the proboscis 

 sheath and two main nerves which run backwards ; no special sense organs 

 are present. No digestive tract is present. 



The AcantJiocephala are unisexual. Extending back from the probos- 

 cis sheath is a prominent band-like structure called the ligament which ends 

 in the hinder part of the body cavity. In the male two ovoid testes are 

 connected with the ligament, the vasa deferentia, with which several glands 

 are joined, passing back to the complex genital opening at the hinder end 

 of the body. In the female the ovary is also in the ligament; the ova 

 escape into the body cavity whence they pass through an oviduct of com- 

 plicated structure to the external opening at the hinder end of the bod3^ 

 Fertilization takes place in the body cavity and the embiyonic development 

 takes place there. The eggs then pass out and in order to develop farther 

 nnist be swallowed by a crustacean or insect. The larval worm then bores 

 through the intestinal wall of this intermediate host and encapsules itself 

 in the body cavity, where it remains until the intermediate host is swal- 

 lowed, probably usually in drinking water, by the final host, to the intes- 

 tinal wall of which it fastens itself. The class contains 4 families, 12 

 genera, and over 100 species. 



Family 1. ECHINORHYNCHIDAE. 



With the characters of the 

 order: several genera. 



1. ECHINORHYNCHUS 0. F. 



Miiller. Body smooth, although 

 often wrinkled after death : nu- 

 merous species. 



E. anguillae Miill. (Fig. 

 366). Body orange-colored, 6 to 

 29 mm. long; proboscis with 8 or 

 10 rows of hooks; neck long: in 

 numerous fresh-water fish; com- 

 mon; Europe; larva probably in 

 Gammarus and small fishes. 



E. ranae Schrank. Body 5 

 to 60 mm. long; proboscis with 12 

 to 20 rows of hooks: in frogs, toads, and salamanders; common; Europe; 

 larva in Asellus. 



Fig. 36G — Echinorhtjnchus anguillae 

 (Siissw. F. Dent.). A, entire worm: 1, 

 proboscis ; 2. lemnisci; 3, proboscis 

 sheath : 4, ligament ; 5, testis ; 6, genital 

 pore ; B, proboscis. 



