ZOOLOGY. 517 



they are next developed, so soon as vessels appear and 

 form a vascular plexus, into foetal involucra or envelopes. 

 These animals are vitellus with the vascular membrane. 



3178. The Absorbent animals are no longer simple 

 vesicles, but large cysts or capsules like the developmental 

 envelopes of the foetus, along with a choroid plexus 

 Involucral, Foetal-animals. 



This choroid plexus does not, however, consist of arte- 

 ries and veins; but is only a ramification of the intestine, so 

 that the vessels are of a lacteal character Absorbent 

 a in inals. 



3179. In these animals there is no longer any egg- 

 shell, but everything has been taken up into the galvanic 

 circle; the shell has itself become organic and life- 

 imbued. Their substance is still mucous or albuminous ; 

 they are still vitellus, though converted into a vascular 

 tissue. 



3180. They therefore cling firmly nowhere ; but swim 

 about freely, like brain- masses converted into radiated 

 cysts. 



3181. Free Mucus-animals, traversed by vascular 

 plexuses, are Acalephce. 



3182. There are Acalepha? which are simply air-sacs, 

 like the air-sacs of ova, to which hang ramified vessels as 

 absorbent tubes Cystic, Tubular Acalephae. 



Others represent hemispheres with numerous absorbent 

 tubes, which concur in the middle of the animal to form a 

 kind of stomach, from which again other tubes pass to- 

 wards the border, in order to elongate into tentacula. Thus 

 the absorbent vessels have become motor and sensitive 

 organs. 



Besides this, many have around the mouth four large 

 lobes, which must be viewed as the antetypes of the sen- 

 tient lobes of the Bivalve Mollusca, 



Lastly, others have a true mouth, which leads to a 

 similar gastric cavity, out of which the same vessels 

 emerge and ramify. Both kinds are called Hutquallen 

 or Medusae. 



There are yet others having the same structure, but 



