Beviews — Agassiz, Seaside Studies. 37 



various species, but tlie facts are presented in such a connection 

 witli reference to the principles of science and to classification, as to 

 give it to some extent the character of a manual of the Eadiata. 

 After treating of the family in general, the author prefixes a general 

 sketch to each of the classes into which the Kadiates are divided. 

 This is followed by an examination in detail of the difi'erent specific 

 forms. 



Whatever adds to our knowledge of recent animals is of importance 

 to the paleontologist. To work well a paleeontologist must begin 

 with the recent and known. The value of such information will be 

 frequently apparent to the intelligent geological reader of this volume. 

 We will close by quoting one illustration regarding a recent dis- 

 covery of Professor Agassiz, not yet much" known in this country. 



" We must not leave unnoticed one very remarkable Hydroid 

 Acaleph, resembling the Polyps so much that it has been associated 

 with them. The Millepore is a coral, and therefore the more 

 easily confounded with the Polyps, so large a proportion of which 

 build coral stocks ; but a more minute investigation of its structure 

 has recently shown that it belongs to the Acalephs. This discovery 

 is the more important, not only as explaining the true position of 

 this animal in the animal kingdom, but as proving also the presence 

 of Acalephs in the earliest periods of creation, since it refers a large 

 number of fossil corals, whose afiinities with the Millepores 

 are well understood, to that class, instead of to the class of 

 Polyps with wliich they had hitherto been associated. But for 

 that we should have no positive evidence of the existence of 

 the Acalephs in early geological periods ; the gelatinous texture 

 of the ordinary jelly-fishes make their preservation almost im- 

 possible. It is not strange that the true nature of this animal 

 should have remained so long unexplained ; for it is only by the 

 soft parts of the body, not, of course, preserved in the fossil condi- 

 tion, that their relations to the Acalephs may be detected ; and they 

 are so shy of approach, drawing their tentacles and the upper part 

 of their body into their limestone frame if disturbed, that it is not 

 easy to examine the living animal. The Millepore is very abundant 

 on the Florida reefs. From the solid base of the coral stock arise 

 broad ridges, the whole surface being covered by innumerable pores, 

 from which the diminutive animals project when expanded. The 

 whole mass of the coral is porous, and the cavities occupied by 

 the Hydras are sunk perpendicularly to the surface within the stock. 

 Seen in a transverse cut these tubular cavities are divided at 

 intervals by horizontal partitions extending straight across the 

 cavity from wall to wall, and closing it up entirely, the animal 

 occupying only the outermost open space, and building a new par- 

 tition behind it, as it rises in the process of growth. The structure 

 is totally difi'erent from that of Madrepores, Astrgeans, Porites, and 

 indeed, from all the Polyp corals, which, like all Polyps, have the 

 vertical partition running through the whole length of the body, and 

 more or less open from top to bottom." (pp. 22, 23). 



