﻿OF THE ACALEPH.£ OF NORTH AMERICA. 287 



occurrence of the other state ; just as those caterpillars which live long in the caterpillar 

 state are more frequently met with than the moth which they produce, the duration of 

 whose life is short ; and vice versa, the butterflies, which live nearly throughout the year, 

 and spend a few weeks only in the caterpillar state, are more often seen in a perfect 

 condition, while the caterpillars are of rare occurrence. 



Another difficulty would seem to be more serious, namely, that there are at least 

 two species of Tubularia, very different from each other, found on these shores ; while only 

 one Hippocrene has as yet been noticed. I am well aware that more than two species of 

 Tubularia have been described, but I should not be in the least surprised, if all the branch- 

 ing and simple varieties were mere forms of two distinct types, one of which has a large 

 crown, and the other a small one, — one a prominent inner tube, and the other a shorter 

 one. The fact that the proboscis in Tubularia is fringed around its opening is greatly in 

 favor of its being the alternate generation of Hippocrene, in which the mouth is also 

 adorned with bunches of fringed or branched tentacles. But the difficulty of more spe- 

 cies would be unanswerable, if we could be positive that we know all the species of Me- 

 dusas occurring along these shores. That this, however, is by no means the case, I ascer- 

 tained during the last summer, when I found (in localities where the two types of Tubu- 

 laria occur simultaneously) no less than four species of Medusa? belonging to four differ- 

 ent genera, which had never been noticed before on the coasts of Massachusetts ; * and 

 one of these new species is closely allied to Hippocrene ; though, from the peculiarities in 

 its tentacles and eye-specks, I am inclined to consider it a peculiar genus, of which I shall 

 say a few words at the close. 



I have had some hope of raising the polypidom type of Hippocrene from eggs of this 

 species, but have been unsuccessful in this respect, though several specimens I had pre- 

 served in glass jars have laid their eggs in captivity. But these eggs are so minute, that 

 with all possible care, and all attention bestowed upon them, I have been unable to pre- 

 serve them so as to watch their growth. The eggs are so minute that it requires a cer- 

 tain magnifying power even to see them, and to watch them in the water after they have 

 been scattered about is almost impossible, as the isolated eggs completely escape the 

 power of the naked eye. 



* For the opportunity of observing so many new marine animals, I am indebted to the liberality of Profes- 

 sor A. D. Bache, Superintendent of the U. S. Coast Survey, who has repeatedly allowed me to avail myself of 

 the surveying vessels under the command of Lieutenant Charles H. Davis, for the purpose of scientific in- 

 vestigations. I cannot allow this opportunity to pass, without acknowledging publicly my gratitude for this 

 liberality, and returning my most sincere thanks to Lieutenant Davis for the kindness with which he has con- 

 stantly assisted me in my researches. 



