LIFE-HISTORY OF BUCEPHALUS HAIMEANUS. 679 
to different fishes, noticeable differences in appearance, those 
in the perch and the bass, as noted above, having progressed 
further in their development than those in the pin-fish. That 
these changes should continue seems most probable. 
Since this is true, is it not possible that all of the forms of 
Gasterostomum which have been described have come from 
similar larval forms, and that the differences which may exist 
have come about during a single generation ? 
When one compares the published figures of— 
G. gracilescens, Wagener, 1858 ; 
» armatum, Molin, 1858. lLevinsen, 1881; Olsson, 
1867 ; 
» crucibulum, Rud; 
, trigle, Van Beneden, 1871; 
» ovatum, Linton, 1899 ; 
» sp. Lt. (from Tylosurus marinus), 1899; 
(the form which I have studied), he is impressed with their 
great similarity. The differences as shown by these investi- 
gators is shght. 
From a limited region Van Beneden described four new 
species, and also found individuals which he referred to two 
old species. 
I have tentatively held the form under consideration as 
G. gracilescens, not only because the more immature 
forms found in Tylosurus agree with the figures of young 
G. gracilescens published by various investigators, but 
also because I believe that most of the species described are 
physiological varieties of this form. The described species of 
Gasterostomum are all to be found in regions from whick 
Bucephalus has been described. 
The Effect of the Parasite on the Oyster. 
From an economic standpoint a consideration of the effect 
of the presence of the sporocysts in the oyster is of import- 
ance. 
The distribution of this parasite is undoubtedly wide. 
