128 ACALEPHS IN GENERAL. Part I. 



There is still another feature among Polyps, which ought to be considered in 

 this connection. Not only do the Halcyonoids, the higher order among Polyps, 

 form compound communities in all their representatives, but we find that these 

 compound communities tend to acquire a marked individual independence, which 

 is fully reached in those types of this order which, like Yeretilluin, Renilla, and 

 Penuatula, move about freely, and these are the highest among the Halcyonoids. 

 A similar tendency to individualization of communities is also observed in the 

 highest Actinoids ; for some Madrepores not only form comjjlicated communities, 

 but exhibit, at the top of their branches, an individual which, though fomiing 

 part of the community, is larger than all the lateral individuals, and gives, as it 

 were, individuality to each branch. 



With these facts before us, it will not be difficult to determine the relative 

 standing of the Rugosa and Tabulata. The Rugosa differ from the Tabulata in 

 having a considerable number of representatives which are simple individuals ; or, 

 when they form communities, these are a loose aggregation of a few individuals 

 maintaining a certain degree of independence : we never find among them communities 

 formed of innumerable closely combined individuals, such as occur among Tabulata, 

 in man}' of Avhich there exists a direct communication laetween adjoining individuals 

 through pores in their walls. I am, therefore, inclined to consider the Rugosa as 

 inferior to the Talndata ; and their prevalence in the oldest rocks and their early 

 extinction in geological times, while Tabulata are continued to this day, confirm 

 this view. The Rugosa seem to me to stand in the same relation to the Lucer- 

 narioids among Hydroids, as the Actiniae stand to the Fungid* among genuine 

 Polyps. And here, again, we have a remarkable analogy between the two types, 

 in the circumstance that Fungida? are the oldest genuine Corals known, as the 

 Rugosa are the oldest type among Hydroids. 



All this is in perfect accordance with the character of the higher Acalephs. 

 As we have seen before, the Ctenophora3 are analogous to Echinoderms ; but 

 Echinoderms have reached a degree in organic complication in which individuality, 

 as such, becomes a character of su^ieriority. In conformity with this analogy, we 

 find that all Ctenophorai are free individuals, and so are the Discophoraj also ; 

 while the free naked-eyed Medusae arising from Hydroids occupy, in that respect, 

 an intermediate position between the higher Acalephs and the lower Hydroids, 

 Avhich form large and highly complicated communities, and bear, in their perfect 

 state, sessile Medusaj buds only. I do not see that any olyection can be made 

 to the rank here assigned to the Acalephs in general. It seems to me to be 

 determined by their whole structure, as well as by their mode of development, 

 and must be considered as the true expression of their natural affinities, if the 

 lowest Hydroids are those in which the hydroid elements prevail over the me- 



