THE DEVELOPMENT OF PAL U DIN A VlVlPAliA. 



Notes on the Development of Paludina vivi- 

 para, with special reference to the Urino- 

 genital Organs and Theories of Gasteropod 

 Torsion. 



Isabella M. Di*iiiiiiiioii<l. 



With Plates 7—9. 



These researches have beeu conducted iu the Laboratory 

 of Comparative Anatomy at Oxford, under the super- 

 intendence of Professor Weldon. They were originally 

 undertaken in order to confirm or correct the account of the 

 coelom and its derivatives given by von Erlanger, and the 

 results obtained are set forth in Part I of this paper. These 

 then led to a renewed study of the whole course of develop- 

 ment with a view to obtaining evidence upon the theories of 

 torsion recently put forward by Pelseneer, Amaudrut, and 

 Boutan. Von Erlanger's account deals only with the organo- 

 geny, and leaves the question of torsion on one side; it is 

 perhaps for this reason that the development of Paludina 

 has lately been sometimes regarded as too much modified 

 and abbreviated to give any clear evidence on this point. 

 Doubtless great modification has taken place owing to the 

 loss of the free larval life; nevertheless, bearing this in mind, 

 it is possible to a large extent so to disentangle the different 

 processes of development which, owing to abbreviation, here 

 go on side by side, as to be able to compare the results 



VOL. 46, FAK'J' 1. NEW SEKIES. {J, 



