318 Professor Agassiz's Zoological Researches. 



make them project. The general cavity of the body is filled 

 with water, which enters by the mouth and stomach, as well 

 as by the nmnerous microscopic pores arranged in vertical 

 sei'ies in the walls, and which issues by the tentacula and 

 these same walls. The produce of digestion constantly 

 mingles with this water ; but as the mouth, stomach, and 

 extremity of the tentacula can be closed at pleasure, the di- 

 luted nutritive fluid may circulate for a long time between 

 the plates of the general cavity of the body and in the tenta- 

 cular tubes, before spreading itself exteriorly, and becoming 

 farther diluted by the introduction of new water. In these 

 animals, then, the same walls serve to elaborate the food, to 

 separate the nutritious fluid, and make it undergo the neces- 

 sary modifications for the purposes it has to fulfil ; functions 

 which, in the higher animals, are devolved on the particular 

 apparatus of circulation and respii-ation. 



I forgot to mention, that, in the same deposit, this same 

 individual produced living young, as far advanced as those 

 from the eggs, many days after their exclusion, and the eggs 

 at very diff"erent degrees of development ; so that this Acti- 

 nia (which I shall describe under the name of Bhoclactinia 

 Davisii) is at the same time oviparous and viviparous. Hav- 

 ing seen many similar successive layings, and having ob- 

 served this fact in two distinct species, I am inclined to be- 

 lieve that it is the ordinary mode of reproduction among the 

 Actinias. 



I shall not speak to you of the numerous genera of Tubu- 

 laria, Sertularia, and Bryozoai'ia, which I have had occasion 

 to examine ; this would lead me into an infinity of details 

 which are not yet sufficiently digested. 



Discarding the sponges from the class of Polypi, as having 

 nothing to do with the animal kingdom, and also the Bryo- 

 zoaria, which are li-ue Molluscs, botli in regard to their or- 

 ganisation and mode of development, this class contains 

 a very natural group of animals extremely like each other ; 

 for, although wo sepai^ate them into two great divisions, the 

 Hydroides and Actinoides, it is not difficult to demonstrate 

 the most intimate analogy between these two types. 



