OP CONCHOLOGY. 125 



Fishes microsthenic ; Placentalia and Reptilia are macrosthenic ; 

 Aplacentalia and Amphibia microsthenic, &c. 



VI. Each Subkingdom is founded on a different fundamental 

 phin, •which is modified in an analagous manner according to their 

 manner of feeding and element of habitation. 



Expl. — Talpa, Gryllotalpa, Lepidoptera, Birds ; Fera, Carabi. 



VII. The nervous system affords characters for distinguishing 

 the Subkingdom ; but only among Mammalia is it sufficiently 

 known to afford the base for Subclasses, (Gyrencephala, Lissen- 

 cephala, Owen.) The Androgyna have among Mollusca the 

 greatest number of nodules upon the nervous ring, which may 

 be considered a character of superiority. 



VIII. The plan of the circulatory system indicates the limits 

 of the Prgeclasses, although it may undergo considerable degrada- 

 tions, for instance, in Leptocardii, or even be wanting without 

 the general plan of organization being changed in a considerable 

 degree, as Taeniae among Platyhelmata, Rhizocephala among 

 Crustacea. 



IX. The generative organs afford characters indicating rela- 

 tive rank and probably the limits of the classes, but are not yet 

 sufficiently investigated from a systematic point of view. 



1. Sexes are separated, with external copulatory organs, 

 which either are a male introraittcnt organ or an organ of re- 

 tension, homologous with the locomotive organs. 



2. The functions of both sexes are united in each individual. 

 Male organ retractile, e.g. Hirudines, Lumbrici; Mollusca andro- 

 gyna,* Platyhelmata.f 



3. Sexes are separated, but without copulatory organs. Teli- 

 osts, Acephala, Annelida. 



4. Hermaphroditism is only a character of specific value. 

 Serranus (Dufosse), Pecten (M. Edw.), Chrysaora (Derbes, Ar. 

 Wright.) 



X. The state in which animals produce their young is of th© 

 highest importance to distinguish the relative rank, although it 

 rarely agrees exactly with the limits of divisions higher than 

 orders. Not all the Marsupialia are provided with a pouch. Not 

 all the Batrachians have the same manner of development, but 

 still it is one of the fundamental characters of the division. 



* The male organ of Pulmonata can scarcely be considered an intro 

 mittent organ, as it only serves as an organ of retension, whilst the sper- 

 matophores are mutually introduced. 



t The Lemniscus of Owen may be considered the male organ. 



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