Scientyk Reviews, 407 



u confirmation of facts previously observed by others. Of the 

 twenty-three species described, two, viz. A. filiformis and A. de- 

 pressa are new, having been discovered by the author himself, the 

 one on the coast of Norway, the other in the Mediterranean. Co- 

 loured representations of a few specimens of Actiniae are given in 

 three very well executed copperplates which accompany the work. 



The method of arrangement adopted by Professor Rapp appears 

 to us certainly to possess considerable merit ; but we doubt much 

 whether, in the actual state of our knowledge, it be applicable in 

 every instance. In some cases the animals are in all respects but 

 imperfectly known ; and of their mode of propagation at least, from 

 which it is proposed to draw their most distinctive characters, we 

 knmv absolutely nothing. In proof of this, we need only refer to 

 the Millepora, which stand among the Exoaria, though the author 

 himself is constrained to admit that their mode of propagation is 

 altogether unknown. By this classification, moreover, animals are 

 included under the name of polypi, which seem to us to differ too 

 much in their structure to be classed together. Between the Hy- 

 dra and Actiniae there are no doubt various transitions connecting 

 them together ; but the more complex structure of the latter 

 would, in our opinion, entitle them with equal justice to be placed 

 among the fichinodermata ; at any rate, it must be sufficient to re- 

 quire their separation from the polypi. 



But however difficult of practical application, no attempt at clas- 

 sification on a new principle is without its advantages. By it we 

 are made to contemplate objects in a diflferent point of view, and 

 are thus led to perceive relations between them which had lain 

 concealed from us before. On this account alone, therefore, the 

 essay of Mr. Rapp would be entitled to credit, and this is much 

 enhanced by the numerous valuable facts and observations with 

 which it every where abounds. 



The work of Eschscholtz treats of those gelatinous marine ani- 

 mals commonly known under the name of Medusae, the different 

 tribes of which are comprehended by naturalists under the general 

 appellation of Acalepha. The author has enjoyed extensive oppor- 

 tunities of studying these animals in a recent state ; and, on com- 

 paring the resiUts of his own inquiries with what was previously 

 known on the subject, he found that they presented so much that 

 was new in regard to the systematic arrangement of the Acalepha, 

 that he resolved, in place of publishing the facts in a detached form, 

 to incorporate them in a work that should contain a complete his- 

 tory of the animals in question, with the classification and descrip- 

 tions of all the species hitherto discovered. 



The species described amount to about two hundred, of which 

 the author has himself examined more than a third. They are ar- 

 ranged into three orders, viz. 



1. Ktenophorae, (Rippenquallen.) With a large central diges- 



VOL. II. 3 G 



