HYDROZOA, 77 



the distinction of four kinds of individuality in 

 the animal kingdom. First, hereditai-y indi- 

 viduality, when from a single egg a single inde- 

 pendent being is produced. Secondly, derivative 

 or consecutive individuality, or " that kind of 

 independence resulting from an individualisation 

 of parts of the product of a single egg ; " as in 

 many Lucernaridce, Corynidce, and Campanu- 

 lariadce. Thirdly, secondary individuality, where 

 the product of one egg multiplies by continuous 

 gemmation, giving rise to an immoveable com- 

 munity ; as in the Sertulariadce, Lastly, there is 

 complex individuality, where a similar but move- 

 able community is formed ; as seen in the Caly- 

 cophoridcc and Physophoridce. In this case, he 

 adds, "the individuals of the community are not 

 only connected together, but, under given cir- 

 cumstances, they act together as if they were one 

 individual, while at the same time each individual 

 may perform acts of its own." 



Others were for regarding the gonophores of the 

 fixed Hydrozoa as the perfect or adult stages of 

 the forms by which they were produced, the whole 

 process being viewed as one of ordinary meta- 

 morphosis. The particular objection just stated 

 applies also to the opinion under consideration, 

 which has, nevertheless, found its advocates in a 

 few writers of distinction. There is, no doubt, 

 some degree of plausibility in a view which consi- 

 ders the fixed Corynid or Campanularid as the 

 young condition of the more complex Medusoid to 

 which, by gemmation, it gives rise. It is now, 

 however, certain not only that the Ccdycophoridce 

 and Physophoridce agree closely in structure with 

 the Hydrozoa just named, but likewise, that they 



