40 THE E^ATUEAL niSTOET EEYIEW. 



establislied by Milne-Eclwards in the well-lmown "Ilistoire Naturelle 

 des Coralliaires " except tliat he has removed the Tabulata and Eugosa 

 of Mihie-Edwards, chiefly formed of Eossil corals, to the place 

 assigned to them among the Hydrozoa by the researches of Agassiz. 

 In his treatment of the complicated phenomena of the life-history 

 of the Hydrozoa and his appreciation of their bearing upon the 

 system, Dr. Cams seems to us to have been very happy. His first 

 order consists of the Medusee (the Steganophthalmata of Forbes, 

 the Lucernarid^e of Huxley, less Lucernaria), his second of the Lucer- 

 naricBy the Calycozoa of Leuckart. For his third and last order he 

 adopts Yogt's name of Hydromedusae, giving it, however, a sense 

 very different from that in which its author used it. The Hydrome- 

 dusce of Dr. Carus include two groups, the Siphonophora and the 

 Hydroidea ; the former described in general accordance with 

 Professor Huxley's views, except that the main division into Caly- 

 cophorida3 and Physophoridae is rejected ; the latter including the 

 whole of the Hydroid Polypes and Naked-eyed Medusae of former 

 authors. Of the sexual Medusoids, whether set free from fixed 

 Polype-forms or produced directly from the ova of similar creatures, 

 an analysis is given in accordance with Gegenbaur's " System der 

 Medusen," but this is only preliminary to the systematic resume, in 

 which the author endeavours to represent the multifarious relations 

 of these perplexing creatures. In this the Hydroidea are divided 

 into two sections, Haplomorpha and Diplomorplia, the former includ- 

 ing those Medusoid forms (Geryonidse, Trachynemidge, ^quoreid^, 

 and Aeginidae) which are developed directly from the ovum without 

 metagenesis, — and the latter, the Polypoid forms which produce either 

 free sexual zooids, or attached and usually more or less Medusoid 

 buds. To the latter group Dr. Carus refers the Tabulate and Eugose 

 Corals, of course provisionally, forming with them a section to which 

 he gives the name of Litliydrodea ; his other sections of Diplomorpha 

 are called Shenotolca (Sertularian and Campanularian polypes) and 

 Gjjmnotolca (Tubularidae, Corynidse, with Hydra). 



That there may be defects in this system can hardly be denied, 

 but it seems to us to approach more nearly towards the production 

 of a true picture of the natural relations of the Hydrozoa than any 

 of its predecessors. 



Indeed as we approach the lower confines of the Animal Kingdom, 

 or of any of its great divisions, a certain difficulty of satisfactorily 

 classifying the objects under consideration seems always to meet us. 



