TRANSMIGRATIONS AND METAMORPHOSES. 198 



Echinodermata, and has had the kindness to send me 

 his original drawings of these singular parasites. 



We have found hoth at Marseilles and at Trieste, 

 says J. Miiller, a new cercaria with a pinnate tail, and 

 two Mack ocular points ; its body is from one-tenth to 

 one-sixth of a line in length, not including the tail, which 

 is twice or two-and-a-half times as long. There is a pro- 

 tuberance just in front of the middle of the body. At 

 each side of the tail there are from twelve to twenty 

 pencils of soft bristles placed on little prominences in a 

 transverse series of six tufts, not regularly opposed to each 

 other. In one specimen, the tail, from its point of 

 insertion to the posterior quarter, is provided with these 

 bundles of bristles ; and in another they are wanting 

 entirely in the anterior half, but exist, on the contrary, 

 on the hinder half. In a third, the bristles have par- 

 tially disappeared, and are reduced to six bundles at the 

 extremity of the tail. This tail presents traces, more or 

 less distinct, of transverse rings. J. Miiller has often 

 seen that the distome, which proceeds from this cercaria, 

 swims freely in the sea, and after having got rid of its 

 tail, could be easily recognized by the two black marks 

 which were then more diffused. 



This cercaria described by J. Miiller recalls to us that 

 which was noticed by Nitzsch on fresh-water shells 

 (Cercaria major) with an annulate and pinnated tail. 



Claparede also took at Saint-Vaast, cercarise the host 

 of which he did not know. This naturalist supposed 

 that this worm could migrate at will. He found there 

 the same cercaria (C Haimeana) on Sarsise and Oceanise, 

 but always sexless. 



The Cercaria setifera of J. Miiller has been found 



