MANY-SUCKERED GROUP 



3439 



cilia, has two eyes, and only a couple of suckers at the hinder end of the body. 

 After quitting the egg the larvae are very lively and restless in their movements, 

 either gliding slowly hither and thither, or swimming with rapidity. If unable to 

 find the fish in whose gills they are destined to live, they grow feeble and perish; 

 but if successful in making a settlement in their necessary surroundings, they grow 

 into the Diporpa (</), which is flattened and lancet-like in shape, and bears a small 

 sucking disc on the under surface, and a conical excrescence on the back. After 

 living some weeks or months in this state, and gaining nourishment by sucking 

 blood from the fish's gills, the worms 

 begin to join together in pairs, one 

 specimen seizing the conical excres- 

 cence of another by its ventral sucker, 

 then, by means of a truly acrobatic 

 feat, the second twists round until it 

 is able similarly to attach itself to the 

 dorsal excrescence of the first, and in 

 this state an inseparable fusion takes 

 place between the suckers and excres- 

 cences involved in the adhesion. An- 

 other remarkable trematode is 

 Anthocotyle merlucti, parasitic on the 

 gills of the whiting, which is repre- 

 sented in B of the illustration. The 

 other worm represented in the same 

 illustration (A} is Dactylocotyle pol- 

 lacki, a parasite on the gills of the 

 pollack. Here the slender front end 

 of the body is much longer than in 

 the last, the trunk gradually expands, 

 and is wide and squarely cut at its 

 posterior extremity, upon which are 

 four pairs of long, stout, stalked 

 suckers. The foremost pair of these 

 seem to correspond to the very large 

 suckers of Anthocotyle, We now come 

 to two species of the present group of 

 trematodes which, by their manner of 



life, lead to the second division of the internal parasitic forms. The first of these 

 {Aspidogaster), found in the interior of the fresh-water mussels, is little known; but 

 our acquaintance with the development of the second (Polystomum) is tolerably 

 complete. This animal, with a roundish .body, is less than half an inch in length, 

 and is easily recognizable by the presence at the hinder end of the body of a large 

 wheel-like expansion bearing three pairs of suckers, between the last and longest 

 pair of which are a couple of strong hooks. In the adult stage this worm lives 

 parasitically in the bladder of frogs. It lays its eggs in the spring, and by thrusting 



A. Dactylocotyle; B. Anthocotyle. 

 (Magnified.) 



