LAMELLIBKANCHIA. 



76 



i n f nwlailVia 3D and is retained in the adult in the 



the anterior end, the two efferent ien«u u anterior end of 



the fact that it also an.es in th .torn _<* t) These tube s, as in 



connection with the aduU, ^f^J^SLaiom «"»" " 8 a °™ tj 



the kidney. , « . ■, 



The Formation of the Heart. In following the development of the 

 „,,,„ of Bojanns, we left the periearaia, «*. = b «* * 



though they also 

 underwent essen- 

 tial modifications 

 of form. After 

 the vesicles have 

 slightly lengthened, 

 they become partly 

 constricted, the 

 outer wall becoming 

 invaginated (Fig. 

 32 A, p). In this 

 way, each vesicle 

 appears to be 

 divided into two, 

 but the division is 

 not complete and 

 the two halves of 

 the vesicle still 

 ■al wall of the lower 

 be recognised (Fig. 



?■ 

 ft. 



B 





u\ 



Fig 32. -Diagram of the formation of the heart in Cyclas 



^constructedlfrom Ziegler's descriptions) a auricle ■■{£ 



B the pericardial invagination which leads to its forma 



tion) ; I intestine; g, vessels opening into the auricles . 

 „. renal funnel; p, pericardium ; v, ventrice. 



communicate with one another. In the venti 

 section, the internal opening of the kidney can 



