318 



INVERTEBEATA 



CHAP. 



result the skin on oue side would be stretched and stimulated to 

 grow, while the skin on the other side would be crushed and its 

 growth inhibited. 



A 







Fig. 252. — Transverse sections throngh the visceral humps of two embryos oi Paludina 

 vivipara of different ages to illustrate the torsion of the organs, the development of 

 the genital organs and their connection with the right kidney, and the lengthening of 

 the visceral hump associated with an increase in length of the liver. (After Drummond.) 



A, younger stage in wliich the gonad is beginning as a thickening of the wall of the pericardium, 

 and in which the left kidney is still distinct. B, older stage in which the gonad is connected with the 

 rudiment of the left kidney. The right kidney has passed completely to the left. Letters as in previous 

 figures. 



Such is, in outline, the organogeny of a Mollusc; and, as 

 mentioned above, Erlanger's work, except in so far as concerns the 

 origin of the mesoderm, has been confirmed by the most recent 

 workers on MoUusca. 



