Tlie anatomy of Lucapina crenulata. 



457 



wall of the visceral cavity. To see the two ventral lobes the stomach 

 must be removed. Here we find that the walls of the stomach are 

 strongly attached to the muscular walls of the visceral cavity by liga- 

 ments, which pass through the liver and genital mass, also supporting 

 these organs. The small end of the stomach usually has one or more 

 large ligaments; while the large end is supported by numerous smaller 

 ones, which also hold the viscera firmly in position. A sphincter-like 

 thickening almost surrounds the small end of the stomach where it 

 enters the intestine (Fig. F S^jh). 



Fig. F. Fig. G. 



Jn. r 



-Er. 



Bds. 



•V^^f^cr^V^^"^^^ 



Ex.r: 



ExL 



M.c 



Fig. F. Stomach, laid open from above. Oe oesophagus, if. d hepatic ducts, Jn in» 

 testine, Sjih sphincter muscle. 



Fig. G. Posterior part of mantle cavity; the ctenidia and rectum are raised to 

 show the external ojDening of the right nephridium Exr, and the position of the external 

 opening of tiie left, E.rL Mc mantle cavity. Bas basibranchial sinus, Ef efferent sinus, 

 Af afferent sinus, A anus. 



From this point on the alimentary canal is about of an equal 

 diameter. It makes a loop forward upon leaving the stomach, then 

 curves back beneath the liver mass, being almost imbedded in it, to 

 the place where the intestine emerges on the right side. Here sur- 

 rounded by the tissues of the right nephridium it again takes a turn 

 backward, this time above the stomach and liver and finally, the 

 rectum being reached, it continues forward through the ventricle of 

 the heart to open into the posterior part of the mantle cavity (Fig. G A), 

 between the ctenidia and directly under the fissure in the mantle 

 and shell. 



Excretory system. The nephridia in Lucapina are very un- 

 symmetrical, the left one being very small indeed, the right very large 

 and extending across the body. The latter kidney light brown in 

 color may be seen very well by removing the dorsal wall of the vis- 

 se)* 



