Chap. II. INDIVIDUALITY AMONG ACALEPHS. 97 



passes away with them ; and that, therefore, while individuals alone have a material 

 existence, species, genera, families, orders, classes, and hranches of the animal king- 

 dom, exist only as categories of thought in the Supreme Intelligence, and, as such, 

 have as truly an indejiendent existence, and are as unvarying, as thought itself 

 after it has once been expressed. 



Returning, after this digression, to the question of individuality among Acalephs, 

 we meet here phenomena far more complicated than among higher animals. Indi- 

 viduality, as Air as it depends upon material isolation, is complete and absolute in 

 all the higher animals, and there maintained by genetic transmission, generation 

 after generation. Individuality, in that sense, exists only in comparatively few of 

 the Radiates. Among Acalephs it is ascertained only for the Cteuophoraj and 

 some DiscophorJB. In others, the individuals born from eggs end by dividing into 

 a number of distinct individuals. In others still, the successive individuals derived 

 from a primary one remain connected to form compound communities. We must, 

 therefore, distinguish different kinds and different degrees of individuality, and may 

 call liercditary individuality that kind of independent existence manifested in the 

 successive evolutions of a single Qgg, ^xo^wvk^^ a single individual, as is observed 

 in all the higher animals. We may call derivative or consecutive individuality that 

 kind of indejiendence resulting from an individualization of parts of the product 

 of a single egg. We have such derivative individuals among the Nudibranchiate 

 MoUusks, whose eggs produce singly, by a process of comjjlete segmentation, several 

 mdependent individuals. We observe a similar phenomenon among those Acalephs, 

 the yoiuig of which (Scyphostoma) ends in producing, by transverse division (Stro- 

 bila), a number of independent free Meduste (Ephyroe). We have it also among 

 the Hydroids which produce free Medusfe. Next, we must distinguish secondary 

 individuality, which is inherent in those individuals arising as buds from other indi- 

 viduals, and remaining connected with them. This condition prevails in all the 

 immovable Polyparia and Hydraria, and I say intentionally in the immovable ones ; 

 for, in the movable communities, — such as Renilla, Pennatula, etc., among Polyps, 

 and all the Siphonophora3 among Acalephs, — we must still further distinguish another 

 kind of individuality, which I know not how to designate properly, unless the name 

 of complex individuality may be applied to it. In complex individuality a new element 

 is introduced, which is not noticeable in the former case. The mdividuals of the 

 community are not only connected together, but, under given circumstances, they 

 act together as if they were one individual, while at the same time each individual 

 may perform acts of its own. 



As to the specific differences observed among Acalephs, there is as great a 

 diversity between them as between their individuals. In some types of this class 

 the species are very unifonn, — all the individuals belonging to one and the same 



VOL. III. 13 



