No. 2.] | THE ORIGIN OF THE SEX-CELLS. 205 
hydroids live upon animal food, and during the summer months 
when they are very prolific, it is not at all uncommon to find 
that these nourishing polyps had swallowed the young of 
Pagurus as they swam out from the shell; in fact, the whole 
colony, at times, assume a decidedly reddish hue, due to many 
of the hydroids having in their digestive cavity the undigested 
brilliantly colored Paguri. It can clearly be seen, then, that 
these hydroids obtain much of their food through their very 
convenient situation upon this Pagurus shell. 
The study of the life history of the Hydractinia has been 
left almost untouched. P. J. van Beneden in 1841 observed 
the ova, which especially interested him, since he was able to 
find all the differentiation in them, which is to be seen in the 
ova of forms higher in the animal kingdom. Stethrill Wright 
in 1857, presented a short paper upon the development of 
Hydractinia, which brings out many salient points in its life 
history, although this paper is quite incomplete from our 
present standard. In this he states that the Hydractinia are 
“oviparous where true ova are discharged from the ovarian 
sacs, and subsequent changes into planaroid and_ polypoid 
forms take place after their leaving the zodphyte.” In his 
general description, he speaks of the ova carried in sporosacs 
that are developed from the hydrorhiza; he having failed to 
observe the blastostyle. 
The development of the gonophore, and the origin of the sex- 
cells has been described by Ed. van Beneden in 1874, and also 
by Weismann in 1883. 
PODOCORYNE. 
A colony resembling the Hydractinia was found in the 
summer of ’90 by H. W. Norris at Naushon, and brought by 
him for identification to Dr. J. Playfair MacMurrich, which by 
microscopical investigation I proved to be Podocoryne Carnea, 
first observed in 1839, and described in 1846 by Sars. In 
addition to the free swimming medusa, Sars speaks of hydroids 
bearing gemmae during March, but as I only had an oppor- 
tunity to observe them in July, and August, I never found these 
organs. 
