52 d. moore, m.d., on Bucephalus Haimeanus 



for themselves, so that the life-history of these organisms may be 

 fully settled. When I first saw M. Lacaze-Dutbiers' paper it 

 was a great pleasure to me to read his account of an organism 

 which had occupied a good deal of my attention, and to recognise, 

 in the description of so good an observer, much with which I was 

 familiar ; and you will see tbat the facts I have observed have 

 been much the same as those recorded by him. I have, however, 

 never found B. Haimeanus in the oyster, although receiving both 

 oysters and cockles from the Hayling oyster beds, where, as they 

 are in juxtaposition, it would appear probable that this organism 

 might be found in both, if parasitic. I have also never found it in 

 cockles containing spermatozoa, but only in those containing eggs, 

 and never before the eggs were fully formed. These statements 

 represent the examination of a large number of these molluscs, 

 and although the explanation of this limitation may be of a local 

 character, yet it had a decided effect in forming my opinion. 

 Before going further, I think it may make the subject clearer to 

 some here if I give a very brief outline of the facts (for which we 

 are indebted to the observations of Nitzch, Siebold, Bojanus, and 

 Steenstrup) concerning one of the Cercarice, whose life -histories 

 have been the most clearly traced. Eliminating minor details, 

 about which differences in opinion exist, it appears to be briefly as 

 follows : — The perfect sexual form of fluke, found in certain water 

 snails, lays eggs which are supposed to develope into a small 

 vermiform organism of a yellowish colour, about two lines in length, 

 which may be found adhering in large numbers to various parts of 

 the snail, in which the distoma is parasitic. After a time the 

 interior of these small vermiform organisms is observed to be 

 occupied with a numerous progeny, which, being set free from this 

 nurse, or sporocyst, and also from the host, appear as freely 

 moving Cercarice in the water ; in this state they have a movable 

 tail, a head furnished with booklets and a sucking mouth ; these 

 Cercarice may be seen attaching themselves to the skin of the snail 

 into which, their tails being cast off, they penetrate more or less 

 deeply, and become encysted in a case of hardened mucus — after a 

 time undergoing a further development into a well-formed 

 Distoma, and then becoming distributed to their appropriate 

 parasitical habitat. Siebold, however, thinks that the free Cercarice 

 may penetrate insect larva*, and await their transference to higher 

 organisms. So that we get first the ova from the Distoma, supposed 



