8 OSBORN. [Vol. XVIIT. 



an elongation of the body ; then the dilatation of the front portion 

 to form a large circular disk, which is applied to the kidney sur- 

 face, sometimes firmly enough to adhere strongly ; then a contrac- 

 tion of the disk, sweeping across the surface of the kidney and 

 gathering up material, which is then seen to be swallowed, move- 

 ments for the purpose taking place in the pharynx ; then the entire 

 body is much contracted, after which the events are repeated in 

 the same order in another place. I have tried to show these facts 

 in Fig. 2, b. 



One might suppose that the fluke would change its position 

 from time to time, but it does not appear ordinarily to do so. To 

 test this I opened an Anodonta and pinned the parts under water 

 in such a position as enabled me to watch the flukes and, to report 

 one case, I found that two flukes did not move at all from the 

 position in which I first found them from 9.30 A. M. of one day 

 till 9.30 A. M. of the day following. In the evening of that day 

 they had approached each other, and on the day following, forty- 

 eight hours after the beginning of the experiment, the kid- 

 ney was dead and decaying, and the flukes were found on the 

 adjacent surface of the visceral mass. 



I found that the flukes bear artificial environments very well. 

 I have removed them from the mussel and kept them in glass 

 dishes covered so as to protect them from the dust, and they live 

 thus for several weeks. They seem equally well ofif in hydrant 

 water or in normal salt solution or in a mixture of the two (equal 

 parts). Flukes have lived thus three weeks and behaved nor- 

 mally. In such case they adhere to a certain spot, never moving 

 from it, and keep going through the motions already described, 

 thereby keeping a circular area around them swept entirely clean. 

 I have also kept mussels in my laboratory aquaria for several 

 months and had them sent me by express from Chautauqua for the 

 sake of the flukes. I found that, in such, most of the systems 

 were normal, but there were indications that the reproductive 

 organs had suffered some disturbance. 



There is a long and important interval in the life-history of 

 Cotylaspis of which nothing is known. As I shall show later in 

 this paper, the development of the eggs from the earliest seg- 

 mentation takes place after the egg has left the parent, from which 



