SOME PROBLEMS OF COELENTERATE ONTOGENY 495 
fundamental contention was inconclusive. Results to be cited 
from various sources will tend to show that the early attempt to 
formulate a general theory of embryogeny on the basis of the origin 
of sex-cells was no less defective and inadequate than it was hasty. 
For some time past phases of my researches have forced the 
impression, which has deepened as the investigations have 
extended, that not a few of the earlier views as to coelenterate 
ontogeny were seriously defective, or absolutely in error at many 
points. Certain of these I have taken occasion to point out from 
time to time, as occasion arose. The purpose of the present paper 
is two-fold: First, to submit accounts of the development of 
several species of Hydromedusae which have been under inves- 
tigation for some time; and secondly, to point out certain errors 
as to the ontogeny of the groups which, from various reasons, 
had become associated therewith. 
MATERIAL AND METHODS 
1. Material. The material upon which the results herein 
described are based (with the exception of that of Pennaria 
australis, for which I am indebted to Mr. Edgar J. Bradley, of 
Australia, to whom my thanks are hereby acknowledged) was 
collected by the writer at various times within the past two years, 
and chiefly in the immediate vicinity of Woods Hole, though 
some of that of Clava was collected at Harpswell, Maine. It is 
a pleasure to express my thanks to the directors of these labora- 
tories for various courtesies. 
Attention will be given primarily to two species of Pennaria, 
and to a single species each of Clava and Hydractinia. Other 
species will be given attention in relation to the several problems 
with which the paper has to do. 
2. Fixation. In my earlier work great difficulty was encoun- 
tered in reference to killing and fixing reagents. For killing my 
first lots of eggs of Pennaria picro-nitric and picro-sulphuric solu- 
tions, then much in vogue, were used; but to my sorrow these 
were found to be almost worthless. This was particularly the 
case with picro-sulphuric. Almost the whole of one summer’s 
