SANGUIFEROUS SYSTEM. 429 



ventricle necessitates that of the auricle to perfect its func- 

 tion, and the cleaving of each produces in succession the tri- 

 locular and the quadrilocular heart of the cold- and warm- 

 blooded vertebrata. 



SECOND SECTION. 



Sanguiferous system of the cyclo-neurose or radiated classes. 



In the radiated classes of animals, as in the earliest condi- 

 tion of the human embryo, vessels alone are developed to 

 contain and circulate the fluids, without the aid of a heart ; 

 and indeed, in the simplest forms, the fluids move in a 

 cyclosis through the general cavity of the body, like the co- 

 lourless blood in the cells of a plant, or the first movements 

 of the globules in the germinal portion of an ovum. This 

 constant slow revolution, forwards and backwards round the 

 interior of the body, is seen in the globules, suspended in a 

 more fluid serum, in the paramacium and other polygastric 

 animalcules, and appears to be produced by vibratile cilia 

 lining the cavity, as all the analogous movements in higher 

 tribes of animals ; and the same minute organs are probably 

 the active agents of the currents of globules suspended in a 

 serous fluid, which are seen in the vascular plexuses of the 

 stipulse and other parts of plants, and around the larger cells 

 which compose their structure. In some of the larger com- 

 pound polygastrica, as the volvox, a distinct plexus of ves- 

 sels, forming a reticulate texture, is seen spread over the 

 whole surface of the body, and apparently destined to con- 

 vey the fluids of the component monads over the general 

 mass of these remarkable aggregate beings. The same active 

 cilia appear to produce the circulatory movements through the 

 ramified and motionless canals of poriphera to nourish and 

 aerate the body, as they obviously effect analogous movements 

 in the bodies of many zoophytes. 



The circulation of the blood in many zoophytes was 

 carefully investigated and described by Cavolini fifty years 

 since, especially in sertularice, plumularm, campanularite, 

 tubularice, and other transparent genera, and his obser- 

 vations have been confirmed and extended by many sue- 



