THE ORIGIN OF THE SEX-CELLS 
IN HYDRACTINIA AND PODOCORYNE ; AND THE 
DEVELOPMENT OF HYDRACTINIA. 
MARTHA BUNTING. 
INTRODUCTION. 
HyprAcTINIA was the name given by P. J. van Beneden 
to a hydroid which was found upon the coast at Ostend in 
1841; so called because he considered it to resemble both the 
hydra and the actinia. It has since been described under 
various names, among which was that of Alcyonium Echi- 
natum by Fleming ; the latter specific name was accepted by 
Van Beneden, and thus, we have Hydractinia Echinata. 
The form found by Louis Agassiz, in 1862, was called by 
him Hydractinia Polyclina, while Leidy also figured a similar 
hydroid, and named his after the European species. Agassiz 
founded his change of name upon very slight differences, among 
which may be mentioned a mouth in the reproductive hydroid, 
which he figures as frequently being opened very wide, and 
serving for the prehension of food. Also, that while found 
upon shells inhabited by Pagurus, it was obtained in great 
abundance in tidal pools attached to the rocks. Although I 
closely studied a large number of serial sections, the mouth 
was seldom demonstrated, but when seen, was extremely small. 
This small opening has also been observed, and figured both 
by Van Beneden and Weismann for the European species. 
While found in great abundance upon Pagurus shell, I was 
unable to find them upon anything else ; the shore would be 
covered by Littorina, upon which, however, no hydroids could 
be observed, but at the same place, when such shells were 
inhabited by Pagurus, they would in most cases be covered 
with these colonies ; thus proving that the conditions in the 
latter were much more favorable for the development of the 
