670 DAVID HILT TENNENT. 
My time has not permitted a completed study of the seg- 
mentation and development of these eggs. Limited observa- 
tions seem to show that the process is similar to that described 
by Schauinsland (51, 1883) for D. tereticolle. 
Note.—When I commenced the anatomical and _ histologi- 
cal work on the marine forms of Bucephalus and Gasterosto- 
mum, an account of which has been given above, I had no 
idea that the forms would prove so similar to the fresh-water 
forms of the same name described by Ziegler in 1883. 
To me one of the chief points of interest in my work has 
been the proof of the practical identity of these forms. . 
So far as possible I have carefully avoided a restatement 
of facts which have already been established by Ziegler. In 
the instances when this has been done it has been for the 
purpose of furnishing a basis for the comparison of the marine 
and fresh-water species. 
An Account oF EXPERIMENTS FOR DETERMINING THE LIFE- 
History or BucepHatus HaArMeEanvs. 
In September, 1902, I began a systematic effort to obtain 
the completed life-history of B. haimeanus. The work was 
carried on simultaneously along various lines. I shall first 
describe— 
Experiments on Oyster Infection. 
It has been noticed, and my observations confirmed the 
reports of others in this respect, that the oysters in certain 
areas were badly infected with the parasite, while in other 
localities cases of infection were comparatively rare. 
One of the problems presented by this condition of affairs 
concerns the manner in which infection is spread. The 
question presented itself, is infection direct, that is, do 
cercariz, or portions of the sporocyst escape from one oyster 
and make their way directly to another oyster ? 
As a means of solving this problem I selected oysters from 
