182 ISABELLA M. DL'UMlMONn. 



may take of this matter, however, we are forced to admit 

 tliat rapid development of the mantle cavity must mean rapid 

 growth in the neighbourhood of its formation ; and we have 

 already seen in the descriptive part how a rapid formation of 

 the mantle cavity takes place between Stages D and E to the 

 original right of the anus, that is, in Biitschli's zone of 

 cessation of growth, and this long before torsion is complete. 

 His view of the late formation of the mantle cavity and its 

 effect upon the position of the organs seems to me no less in 

 entii-e contradiction to einbryological fact. The mantle cavity 

 is not formed by any means so late as ]3utscbli would put it ; 

 it takes its origin, in fact, almost simultaneously with the 

 first appearance of torsion, and is, as we have seen, strongly 

 developed before we reach Stage F. Finally, it is, of coui'se, 

 impossible that its formation should have the effect attributed 

 to it by Biitschli unless we regard it altogether as an in- 

 vagination, which we have not sufficient evidence for doing. 



All the above remarks apply, also, to Plate's theory, since 

 he accepted Biitschli's in its main features. The former's 

 suggestion, however, that the liver is the first cause of 

 asymmetrical growth is an interesting one, and must be 

 further examined. His working out of the later stages of 

 development, the formation of the hernia, and the production 

 of the coil find no support in embryology. A hernia, indeed, 

 is formed on the left side in the development of Paludina, but 

 this is of quite a different nature from that described bj^ 

 Plate, as a comparison between his figures and mine will 

 show; for whereas in his theoretical form the hei'nia contains 

 only the livei- of one side, and is at the same time the 

 beginning of the coil of the visceral hump, the bulging 

 out of the side of the body in Paludina is, as the figures 

 show, equivalent to the once symmetrical apex of the visceral 

 hump, aud contains the stomach as well as the liver. It 

 is, moreover, in no way comparable to the formation of a true 

 coil, which is formed by a distinct outgrowth of the liver at a 

 later stage (cf. figs. 13 and 16 with fig. 17). 'i'he coil in 

 Palndina dt)es not begin till torsion is nearly e()m])lete, and 



