522 BIOLOGY. 



rounded by a watery fluid within the widely-expanded 

 chorion and amnion, so does the abdominal pouch hang 

 within the pallia! cavity, or in the wide, water-full chest. 



3203. In the abdomen there is still only the ovarium, 

 and that indeed very large. There are properly two 

 ovaria, each of which, according to my observations (vid. 

 Gottinger Gelehrte Anzeigen, 1806. Stuck 148), opens 

 laterally under the shoulder-muscle and gives exit to the 

 ova, which then enter within or between the branchial 

 fringes, in order to be there developed. 



3204. Here the respiratory organs are still at the 

 same time a kind of uterus. The ova may be oxydized 

 therein, like the embryo is in the uterus. These branchiae 

 are probably still to be compared with, or designated 

 as, sexual branchiae. 



3205. In the back of the shoulder these animals have 

 a highly vascular organ with two excretory passages, 

 which open near to the orifices of the oviducts. I for- 

 merly regarded it as a kidney, but, according to more 

 recent observations, it should be a testis. In the anterior 

 part of the foot there is frequently situated a gland 

 which ejects a gelatinoid moisture, which hardens into 

 glutinous filaments the byssus or beard. It is probably 

 a memento of the tentacula of the Acalephae. There 

 is besides also an organ in the feet of many Bivalve 

 Mollusca, which occasionally squirts a watery juice out 

 to a great distance. I have occasionally found this organ 

 in our Teichmuschel. Its signification is probably the 

 same as that of the preceding organ. 



3206. The organization of the Bivalve Mollusc can be 

 thus most distinctly described ; it is an abdomen, wherein 

 is an intestine with mouth and anus, a liver and a double 

 ovarium ; upon the sides of this abdomen are situated 

 the branchiae in the form of four laminae ; around the 

 branchiae and the abdomen is the pleura or mantle, which 

 is always open posteriorly. 



3207. The mouth is placed directly at the anterior 

 extremity of the abdomen, is devoid of neck and head, 

 as also salivary glands ; it is consequently not a true 



