5:20 BIOLOGY. 



Class 4. Venous, Ovarial Animals. 



3188. With the protrusion into view of the vascular 

 system, the veins are chiefly developed along with their 

 principal organ., the liver, as being the bond of union 

 between the circulation and the intestine. 



3189. The animals, which first bring to bear in addi- 

 tion to the intestine a liver, are the Bivalve Mollusca. 



3190. With the veins arteries also originate, but with 

 a preponderance of venosity or the venous character. The 

 blood is lymphatic, colourless. 



3191. The cardinal venous organ or the liver evokes 

 also into existence a corresponding organ of respiration, 

 namely, free branchiae with the tegumental form bran- 

 chial laminae or leaves. 



3192. In the middle between the branchial laminae 

 and the liver, the heart is evolved ; this organ comprising 

 always a ventricle with an auricle, but consisting of a 

 venous, membranous tissue almost devoid of fibres. 



8193. The first heart is in other respects arteriose ; it 

 receives the blood from the branchiae and transmits it to 

 the liver as well as to the remaining parts of the body, 

 from which it proceeds directly to the branchiae without 

 entering any venous or right heart. 



3194. In these animals, as is well known, four bran- 

 chial leaves lie externally on the belly, which includes 

 the intestine with a large liver, and hangs together with 

 the branchiae as a separate purse within the mantle. 



3195. In the Mussel a structure originates for the 

 first time, which can be compared with a thoracic or 

 pectoral cavity. What covers the branchiae, must stand 

 in the signification of the thorax or chest. The pallium 

 or mantle of the Mussels is pleura. 



3196. Their shells are branchial opercula (as in the 

 Fishes). They are secretions from the mantle, and every- 

 where accompany the branchiae. 



3197. The locket or hinge of the shell-valves corre- 

 sponds to the rachis or spina dorsi, as is especially distinct 

 in the Teredines or "ship-worms." 



