234 



PLATYHELMINTHES. 



FIG. 186. a, egg with embryo of Polystomum 

 integerrimum ; &, larva of same. Dk oper- 

 culum (after Zeller). 



hooks, and of the three pairs of suckers upon the posterior disc. The young 

 Polystomum, eight weeks after the migration into the branchial cavity, at the 

 time when the latter begins to abort, passes through the stomach and intestine 

 into the bladder, and there only becomes sexually mature after three or more 

 years. In some exceptional cases, and always when the larva has passed on to 

 the gills of a very young tadpole, it becomes sexually mature in the branchial 



cavity of the latter. The forms then 

 remain very small, are without the 

 vaginae and uterus, and die after the 

 production of a single egg, without 

 e*er getting to the bladder. 



Fam. 1. Temnocephalidae. With 

 4 to 12 tentacles at the anterior end, 

 and a posterior sucker without hooks 

 or marginal membrane. The integu- 

 ment consists of a cuticle, epidermis, 

 and basement membrane ; in some 

 cases it is, in part, ciliated. There 

 are rhabdites in the tentacles. Mouth 

 subterminal, a muscular pharynx (ab- 

 sent in Craspedella),a,nd an unbranched 

 intestine. A pair of contractile ex- 

 cretory sacs opening anteriorly and 

 dorsally. Genital pore single, ventral, 

 and posterior ; it leads into an atrium, 

 which receives the opening of the uterus and the penis. Eggs with stalk-like 

 appendages, by means of which they are sometimes attached. They live as 

 external parasites on Crustacea, Chelonia, and Mollusca of fresh waters, and 

 feed on Infusoria, small insect-larvae, Rotifers, and Crustacea. They have been 

 found in Australia, New Zealand, Malay Archipelago, S. America, India, and 

 may be regarded as connecting links between the Turbellaria and Trematoda. 

 Temnocephala Blanchard ; Craspedella Haswell. 



Fam. 2. Tristomatidae. With flattened, discoidal, or elongated body ; with 

 two lateral anteriorly-placed suckers, and one large posterior sucker, often pro- 

 vided with radiations and hooks. Parasitic on the skin or the gills of marine 

 fishes, or on the bodies of parasitic marine Crustacea. 



Sub-fam. 1. Tristomidae. With flat body, two suckers, and a large 

 ventral sucker ; genital opening and opening of vagina usually on the left. 

 On the skin and gills of marine fishes. Nitzschia v. Baer ; Epibdella 

 Blainv. ; Phyllonella v. Ben. and Hesse ; Trochopus Dies. ; Placundla 

 v. Ben. and Hesse ; Tristomum Cuv. ; Acanthocotyle Montic. ; Encotyllcibe 

 Dies. 



Sub-fam. 2. Monocotylidae. With flat body. Without lateral suckers, 

 with small ventral sucker. Genital opening median, vagina paired. On 

 skin, gills, or in cloaca of marine fishes. Pseudocotyle Ben. and Hesse ; 

 Calicotyle Dies. ; Monocotyle Tschbg. 



Sub-fam. 3. TTdonellidae. With cylindrical body, with lateral suckers, 

 and large simple ventral sucker. On parasitic Crustacea. Udonella Johnst. ; 

 Echinella v. Ben. and Hesse ; Pteronella Ben. and Hesse. 

 Fam. 3. Polystomatidae. With a more or less distinctly marked-off adhesive 



