434 REVIEWS. 



bibliographical citations scattered throughout its notes cannot fail to 

 prove useful for reference, even in the hands of experts. 



But the second chapter, on Acalephs as a Class, more fully de- 

 mands our attention. The nine Sections into which it is divided are 

 named as follows : — 



Section 1. — Mode of determining the natural limits of the class. 



„ 2. — The different animals referred to the type of Eadiata. 



„ 3. — The classes of Eadiata. 



„ 4. — Morphology and nomenclature. 



„ 5. — Individuality and specific difference among Acalephs. 



„ 6. — Natural limits of the class of Acalephs. 



„ 7. — Gradation among Acalephs. 



„ 8. — Succession of Acalephs. 



„ 9. — Classifications of Acalephs. 



We have quoted the names of these Sections at length, not be- 

 cause it is our intention to notice each, seriatim, but from a desire to 

 afford the reader, who is not already in possession of Professor 

 Agassiz' work, a faithful transcript of its general contents. This 

 having been done, we shall, without following to its extremest details 

 the arrangement which he has laid down, choose from the entire 

 chapter such portions of its contents as seem best fitted for comment, 

 selecting alike those on which we agree with, or are constrained to 

 differ from, their distinguished author. 



First, then, we find that Professor Agassiz is in direct opposition 

 to those naturalists who, following Prey and Leuckart, have pro- 

 posed to place in a distinct sub -kingdom, under the name of Coelen- 

 terata, those so-called Badiate animals in which a well marked body- 

 cavity communicates freely with the digestive sac, whensoever the 

 latter appears distinct. He maintains " that it is an exaggeration of 

 their affinities to unite, as Leuckart has done, and as most G-erman 

 naturalists now do, the Polyps and Acalephs in one and the same 

 great division under the name of Coelenterata." — " I shall presently 

 show [he adds] that all the true Polyps and all the true Acalephs 

 may naturally be grouped with the two characteristic representatives 

 of their respective classes, alluded to in the preceding section ; and 

 that, in connection with the Echinoderms, they constitute one of the 

 four great types of the animal kingdom, characterized by a peculiar 

 plan of their structure, founded upon the idea of radiation ; and that 

 the anatomical differences exhibited by the Echinoderms do not 

 justify us in considering them as a distinct type. The latter are, in 

 reality, only another class of Eadiata, as a comparison of any of the 

 flat Echinoids, such as the Echinarachnius, with an ordinary Medusa, 

 say the Aurelia, readily shows ; Echinus being, as it were, a Medusa, 

 the soft disk of which is charged with limestone particles."* And, in 



* Pp. 40-1. 



