646 DAVID HILT TENNENT. 
believed B. cuculus to be more in accord with the observa- 
tions of von Baer and Siebold on B. polymorphus than with 
those of Lacaze-Duthiers on B.haimeanus. In this opinion 
he was, it seems to me, to a great extent, justified. But with 
the aid of the additional light which Huet (29) has shed upon 
B. haimeanus, and from my own observations I am convinced 
that, as Braun (88) has already suggested, B. cuculus and 
B. haimeanus are identical. 
The rigidity of the tubes which McCrady described, I have 
never been able to observe; on the contrary, I have found 
the tubes to be soft and yielding. 
Lacaze-Duthiers called attention to the differences between 
B. haimeanusand B.polymorphus. Aftera consideration 
of these differences with Huet’s modification of Lacaze- 
Duthiers’ description, it is readily seen that, aside from the 
fact that the one is a marine and the other a fresh-water 
form, the chief difference is that one has long and the other 
short tails. Since the date of Lacaze-Duthiers’ observations 
(1854), when von Baer’s figures and descriptions (1828) were 
his chief source of information concerning B. polymorphus, 
Ziegler’s most excellent account of this form has appeared 
(1883). 
With the aid of the further data at my command it at once 
becomes apparent to me that the only difference in structure 
in the two forms is that of the shape of the tails, and this 
difference is most evident only when the tails are in an 
extended condition. 
The shape and structure of the body with the tails removed 
is identical. 
Observations onthe Free Swimming of B. haimeanus. 
The most abundant source of supply for cercariz of all 
stages has been the sporocysts which occur within the oyster. 
Free swimming stages may also be obtained, though never in 
abundance, by towing with a fine-meshed net in the vicinity 
of the oyster beds. I have also obtained them by placing 
oysters, which I suspected were infected, in aquaria, when 
