The life histoiy of Diplodiscus temporatus Staffobd. 617 



The behavior of these last mentioned worms argues against there 

 being- any phj'siological difference between the digestive juices of 

 the frog and tadpole whicli would account for the migration and 

 encj'stment of the j^oung worms in Prof. Conklin's experiments. 



Part III. 

 Embryological. 



1. The origin of the partheuogenetic eggf<. 



The earliest papers dealing with this question, since they were 

 published before it had been definitely established that every cell 

 comes from a preexisting cell, are of historic interest only. As late 

 as the middle of the past century Moulinié (1856) and Pagen- 

 STECHER (1857) describe „endogenous cell formation" as being the 

 mode of origin of the germ cells in the sporocyst and redia of the 

 Malacocotylea. 



Wagener (1866) traced the origin of the germ cells to cells 

 in the body wall of the sporocyst which become differentiated from 

 the surrounding cells, and finally take on the characters of germ cells. 



Leuckart (1882) concluded, from his studies of the life histor}' 

 of the liver fluke, that the germ cells in the nurse generations may 

 be traced directly to the egg. His idea is that they are embryonic 

 cells which have not become at all differentiated in the formation 

 of the sporocyst; but have come over in the body cavity of that 

 generation. 



Thomas (1883), working on the same form which Leuckart 

 had studied, came to the conclusion that the germ cells may be 

 formed either in the manner described by Leuckart, or that then 

 may arise from cells in the body wall. 



BiEHRiNGER (1884) dcscribes their origin in the body wall. 



Schwarze (1886) supports the view of Leuckart: That the 

 germ cells may be traced directly to the egg, without their having 

 undergone any differentiation. 



The later workers on this subject: Looss (1892), Reuss (1903), 

 Haswell (1904), Tennent (1905) and Rossbach (1906) are agreed 

 that the gei'm cells in the nurse generations arise in the body wall. 



Looss, however, apparently considers them to be undifferentiated 

 cells which are localized in a particular part of the sporocyst. 

 In the summary of his paper he says: „Die Keimprodukte nehmen 



