32. The American Naturalist. [January, 
tions were made, but it seemed highly probable that the canals 
arose after the manner described by Lang, (op. cit. p. 73.) 
. The development of the manubrium calls for no special 
account. Its origin is illustrated in fig. 9, it is also shown in 
fi 
g. 3. 
The origin of the mouth is simply through the rupturing of 
the terminal walls of the manubrium, and was observed 
in several cases, and seems to be after the method common 
throughout the order so far as known. 
There is not the least difficulty in obtaining the young 
medusa or in keeping them alive in aquaria for a considerable 
period of time. We had them as long as fifteen days and 
examined them constantly, but we did not succeed in rearing 
them to maturity. At the time of their liberation from the 
hydroid stock the reproductive organs had not yet made their 
appearance.’ Perhaps a later study of this creature will disclose 
a way in which this important link in the life history can be 
discovered. Until this important fact, the definitive form of 
the medusa, is supplied, the generic affinity of the species must 
remain in uncertainty. There are indications enough, however, 
to justify its provisional assignment to the genus Perigonimus 
of Sars. Not only are the structure of the hydroid stage and the 
structure of the young medusa, in favor of this, but this species 
shares with nearly all of the remaining members of the genus 
the habit of commensalism. Thus P. repens is found on the 
shells of the hermit crab, P. minutus lives on the shells of Tur- 
ritella, P. vestitus is attached to the shell of Buccinum, and P. 
repens is reported from the shells of Libinia in the British 
Islands. The form we are now considering, while it is generic- 
ally related at least in the hydroid and early medusoid stage 
to the Genus Perigonimus, is not, so far as we have been able to 
learn, specifically related to any described species. We have, 
therefore proposed to give it the name Perigonimus jonesii, to 
‘commemorate the founder and constant friend of the Cold 
Spring Biological Laboratory, Dr. Jones. The great luxuriance 
In one instance, figured in No. 12, one of the tentacles was bifid. It was distinctly 
double from the point of its origin and was plainly a monstrous character rarely found. 
Each portion of the tentacle was moved independently but both tended to be retracted 
together on stimulation. 
