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XLIY. — Contributions To the Natural History of the Unhid 

 States of Ameuita. By Louis Agassiz. Vol. III. Boston, 1SG0. 



The third volume of Professor Agassiz' greal work, or rather series 

 of works, on the Natural History of the United States, not many 

 months since issued to its numerous subscribers, contains the com- 

 mencement of his "Second Monograph," which treats of the 63asG < I' 

 Acalephs. 



On the title-page it is stated that the contents of* this Monograph 

 will be arranged under live Parts, viz. : — 1. Acalephs in general. — 

 2. Ctenophora?. — 3. Discophorae. — i. HydrmdaB. — 5. Homologies of 

 the Radiata; the whole to be illustrated with forty-six plates. 



In the volume before us the First of these Parts is brought to u 

 conclusion ; the second, nearly so. Prom a perusal of the table ot 

 contents alone, it might appear that this Part, likewise, had been en 

 tirely finished, but, in the text, Professor Agassiz alludes, more than 

 once, to various observations of his own on the development of the 

 Ctenophora, the promised details of which are not given. But it 

 may be that the author intends to notice these, not at the end of the 

 Second Part, but rather in the course of the Fifth, when the homolo- 

 gies of all the Radiata come to be finally considered. We propose, 

 therefore, for the present, to postpone our remarks on Part II., 

 hoping, in a future number, to discuss in some detail the writings, not 

 only of Professor Agassiz, but also of various other naturalists, on a 

 group so worthy of special treatment as the Ctenophora, the study 

 of whose structure and development has yielded, within the last ten 

 years, results of greater value to the skilled investigator than those 

 which he could boast of having gained, up to that period, from the 

 time that Zoology became a science. 



The First Part of the Second Monograph, with its 152 quarto 

 pages, includes two chapters, of which the first is entitled "Historv 

 of our Knowledge of the Acalephs," while the second treats of 

 " Acalephs as a Class." 



The subject-matter of the first chapter, containing but 35 pages, 

 is discussed under the five following Sections : — 



Section 1. — Period of Aristotle and the Roman Naturalists. 

 „ 2. — The naturalists of the sixteenth and seventeenth 

 centuries. 

 3.— The naturalists of the eighteenth century. 

 „ 4. — The systematic writers and anatomists. 

 „ 5. — Embryological researches upon Acalephs. 



Its contents will be read with much interest, especially by those 

 who are not well versed in this department of Zoology, to whom the 

 large amount of historical information which it embodies is presented 

 in a form at once pleasing ami instructive, while the numerous 



