158 



forming a crop ; in others it is simply enlarged previously to enter- 

 ing the liver mass. The stomach is of two forms ; one, as in D. tuher- 

 culata, is very large, receiving the oesophagus behind, and giving off 

 the intestine in front, and lying in advance of the liver ; the other is 

 received within the mass of the liver, and is very small. The liver 

 in all is bulky, mostly bilobed, and variously coloured, and pours its 

 secretion by one or more very wide ducts into the cardiac end of 

 the stomach. A small laminated pouch — a rudimentary 

 is attached in some species to the cardiac, in others to the pyloric 

 end of the stomach. The intestine is short, of nearly the same 

 calibre throughout, rather sinuous in its course, and terminates in a 

 nipple-formed anus in the centre of the branchial circle. 



The Reproductive Organs are male, female and hermaphrodite. 

 The male organs consist of penis and testis ; the latter is connected 

 with the former and with the oviduct. The female organs are, ova- 

 rium, oviduct, and mucus-gland. The ovarium is spread over the 

 surface of the liver in the form of a branched duct with terminal 

 ampullae. The oviduct terminates in the mucus-gland. The an- 

 drogynous apparatus is a tube or vagina opening from the exterior 

 into the oviduct, having one or two diverticular spermathecse com- 

 municating with it in its course. On the right margin of the body 

 near the front is a common opening, to which converge the three 

 parts of the reproductive organs. The spermatozoa are developed 

 within large and fusiform spermatophora, and are observed in the 

 spermathecee, oviduct and ovary. 



Organs of Circulation and Respiration. — The circulatory organs 

 are, a systemic heart, arteries, lacunse and veins. The existence of 

 true capillaries in the liver-mass seems probable. A second heart — 

 a ventricle, having a portal character, is also described. The systemic 

 heart lies immediately beneath the dorsal skin, in front of the respi- 

 ratory crown, and comprises an auricle and ventricle enclosed within 

 a pericardium. In the systemic circle the blood is returned to the 

 heart without having passed through the special respiratory organ. 

 It is that blood only which is returned from the liver-mass that 

 circulates through the branchiae. 



The authors conclude from their observations, that in the Mol- 

 lusks there is a triple circulation : first, the systemic, in which the 

 blood propelled along the arteries to the viscera and foot is returned, 

 with the exception of that from the liver-mass, to the heart through 

 the skin ; there it becomes partially aerated, the skin being provided 

 with vibratile cilia, and otherwise adapted as an instrument of re- 

 spiration ; second, the portal, in which venous blood from the system 

 is driven by a special heart to the renal and hepatic organs, and 

 probably to the ovarium, where it escapes, doubly venous, with the 

 rest of the blood which has been supplied to these organs from the 

 aorta, and which is therefore only singly venous, to the branchiae ; 

 third, the branchial circulation, in which flows only the more dete- 

 riorated blood brought b}"" the hepatic vein, but in which also that 

 blood undergoes tlie highest degree of purification capable of being 

 effected in the economy, namely in the special organ of respiration. 



