1877.] 171 [McCrady. 



female only upon the discharge of the male direction-cells; up to that 

 time it contains the elements of both sexes. Likewise all the cells of 

 the body must be both male and female since they arise by asexual 

 division from an impregnated egg, or a cell in which the sexes are 

 united. It is important from this standpoint to know whether in the 

 development of the spermatozoa the mother cell breaks up into two 

 portions, one of which becomes the male part, while the other re- 

 mains separated. There are but few observations which can be used 

 here, but those few fulfill our expectations, for they describe a "Mut- 

 terkern" (female element?) which remains behind and is aborted, 

 while the numerous spermatozoa-nuclei continue their life inde- 

 pendently. 



It is curious that the male elements are always more numerous 

 than the female; in the Infusoria the nucleoli exceed in number the 

 nuclei, in eggs there are usually three direction cells, and from one 

 MutterJcern there arise numerous spermatozoa heads. 



It is further to be added that the theory above defended permits 

 a new hypothesis of parthenogenesis, namely: that it is a special 

 form of asexual reproduction or division. 



Prof. John McCrady spoke of the value of many of Mr. 

 Minot's suggestions, and indicated some points on which 

 he held different views. He also presented the following 

 papers : — 



A Provisional Theory of Generation. By John McCrady. 



The course of development in animals is generally admitted to be 

 one of differentiation, such that normally the more highly specialized 

 forms succeed to, and arise from, the less specialized, the heteroge- 

 neous following the homogeneous, the complex superseding the sim- 

 ple. Even Harvey, in the infancy of our modern embryology, 

 perceived and expressed this truth, though he did not make it a 

 conspicuous feature of his theory, reserving that prominence for his 

 peculiar conception of Epigenesis. Von Baer, who, however, made 

 the unfortunate mistake of asserting that the Special is derived from 

 the General — substantially embraced and maintained this, the true 

 doctrine. Since that time it has met with general, though often 

 silent acceptance, and has been recently adopted by Mr. Herbert 



