REVIEWS—CONTRIBUTIONS TO NATURAL HISTORY. 169 
REVIEWS. 
Contributions to the Natural History of the United States of America. 
By Louis Agassiz. Second Monograph, in five parts:—I. Aca- 
lehps in general; II. Ctenophore ; III. Discophore; IV. Hy- 
droide; V. Homologies of the Radiata: With forty-six plates. 
Vol. Ill. Boston: Little, Brown and Co. London: Tribner, 
and Co. 1860. 
Every lover of nature will watch with interest the progress of this 
great work and feel grateful to its illustrious author for opening his 
stores of curious and valuable information, which it has required 
genius, enthusiasm, indomitable industry, and long experience to bring 
together, apply and make available as he has done. The second 
monograph, of which the first volume is now before us, relates to the 
Acalephe, sea-nettles or jelly-fish, a class of the Radiata branch, or 
sub-kingdom of the Animal Kingdom, to which it appears that the 
author has devoted much attention, and which, consisting chiefly of 
marine animals difficult to preserve and rarely seen in museums, is 
less known to persons of general information and even to many 
intelligent naturalists, than almost any other that could be named. 
Information respecting it founded on an intimate acquaintance with 
all that has been done by others, joined with most important original 
observations, applied in a truly philosophic spirit, must be propor- 
tionably acceptable. 
After an historical introduction referring to all that has been done 
on the subject from the earliest time to the present day, our author 
proceeds to the determination of the natural limits of the class, and 
thence of the sub-kingdom or branch of the Animal Kingdom to 
which it belongs, examining the question whether the so-called 
Coelenterata are really separable from the Echinodermata as a 
distinct branch. He decides this question on evidence satisfactory 
to us, setting aside the sub-kingdom Ceelenterata and establishing 
three classes of Radiata: Echinodermata, Acalephe, and Polypifera, 
but proposing some changes in the limits of the two last-mentioned 
classes which deserve attention and have much probability in their 
favour. 
It is a highly interesting and curious discovery of recent times 
that whilst certain Acalephe in their early stages of development, 
assume the Polype form, the lowest division, as they were believed 
to be, of Polypes called Hydroids, most of them are found to produce 
