TREMATODES 171 



L. folium Verrill. Body very changeable, 25 mm. long and 15 mm. 

 wide, yellowish or pink in color; ocelli very numerous, small, and incon- 

 spicuous: New England coast. 



Suborder 2. COTYLEA. 



Polyclads with a sucker in the ventral surface behind the genital 

 pores: 4 families with about 110 species. 



Family PEOSTHIOSTOMIDAE. 



Body elongate and without tentacles; cerebral ocelli on the anterior 

 margin of the body; mouth immediately behind brain; pharynx long and 

 tubular: 1 genus. 



Prosthiostomum Quatrefages. With the characters of the family: 

 8 species. 



P. gracile Girard. Body thin and translucent, yellowish-Avhite in 

 color, 4 mm. long and 1.25 mm. wide; ocelli in 4 groups: New England 



Class 2. TREMATODES.* 



The flukes. Soft, flat or round worms which live as parasites on 

 the skin or gills of fishes and other aquatic animals or in the internal 

 organs of vertebrates and also of many invertebrates. The smallest are 

 of microscopic size, the largest may be a number of centimeters in 

 length. The outer surface of the adult body is an unciliated cuticula in 

 which suckers and chitinous hooks or spines are present, which enable 

 the animal to fix itself to its host. No body cavity is present, the 

 spaces between the organs being filled with the vesicular parenchyma. 



The mouth is at the fonvard end of the body (except in Bucephalus) . 

 The intestine is, with a few exceptions, bifurcate and is without anal open- 

 ing : the food consists of the blood and other juices of the host. The excre- 

 tory system consists of two main portions, the excretoiy vesicles and the 

 excretory tubules. The latter ramify throughout the parenchyma and end 

 with flame cells. The former consist of a pair of lateral canals which 

 receive the tubules and open to the outside through a pair of anterior pores 

 in the Monogenea and a median posterior pore in the Digenea. The nerv- 

 ous system consists of a pair of ganglia just back of the mouth which 

 are joined with each other by a commissure and of nerves which pass to 



* See "Plathelminthes, I. Trematodes," by M. Braun, Bronn's Klassen, etc., 

 Bd. 4, p. 306, 1892. "Die thierischen Parasiten des Menschen," by same, 1903. 

 "Illustrated Key to the Trematode Parasites of Man," by C. W. Stiles, Bull. No 

 17, Hyg. Lab., Treas. Dept., 1904. "Index Catalogue," etc., "Trematoda," by same, 

 Bull. No. 37, same, 1908. "Trematodes," by M. Liihe, Die Susswasserfauna Deutschl., 

 1910. 



