McCrady.] 180 [Dec. 3, 



tive organ found it filled with the fibres " of our parasite. It must be 

 borne in mind, however, that the standard of comparison here is the 

 degree of fat usually retained by healthy oysters in summer, and 

 this is far below what they exhibit in winter. On the whole, all 

 oysters may be said to sicken during the time of reproduction, and I 

 do not think that the individuals I have found thus infested, could be 

 said to be much more sickly than they would have seemed from the 

 effects of their own reproductive processes. In the one case they 

 seem to give their winter's gain to the development of their own off- 

 spring, in the other, to this cuckoo-like worm. In all probability the 

 oyster is completely freed from its intruding guest before the winter 

 sets in. Such fibre* in such number, if introduced with an oyster into 

 the mouth of man, would probably soon make themselves known as 

 something very different from the oyster itself, and yet I have never 

 heard of their being noticed in winter, notwithstanding the enormous 

 consumption of these animals as foodt The fact also that Claparede 

 found a Bucephalus (which he identifies with B. Haimeanus under the 

 name of Cercarid 1 Haimeana) on the coast of Normandy, between the 

 middle of July and the end of September, freely swimming in the 

 sea by means of exceedingly lively strokes of the long appendages, 

 which I have called tentacula for want of a better name, seems to 

 indicate that in the latter part of the summer these parasites abandon 

 their temporary abode in Ostrea edulis and Cardium rusticum, perhaps 

 to seek another; as even in this more mature condition, Claparede 

 found no traces of sexual organs, and but little advance upon the 

 simple structure figured by Lacaze-Duthiers. My own observations 

 were all made in the latter part of July. I do not find any record of 

 the time of Lacaze-Duthiers' observations. • 



in its free condition Claparede several times found this Bucephalus 

 attached to the underside of the disks of Sarsias and Oceanias, and 

 in one instance, probably by some accident, the long tentacula had 

 been lost. He saw, however, nothing to indicate that the Medusas 

 furnished for it more than a temporary harborage. 



In Mnemiopsis Leidyi, A. Agassiz has frequently observed " a long 

 flesh-colored, cylindrical worm, with five longitudinal white lines 



1 Pagenstecher asserts that these larvae are not true Cercariae, and that while a 

 Distoma may develop from their body, their tentaculiform extremity develops 

 anew into a germ-sack. I know not on what facts this statement rests. I quote it 

 from Cobbold's Entozoa, p. 30, having not yet seen Pagenstecher's " Trematoden 

 und Trematoden-Larven." 



