812 



THE AMEBIC AN NATURALIST [Vol. XLII 



not mean the earliest visible developmental stage, but the repre- 

 sentative of the organ in the germ-plasm. 



In the introduction Correns notes that the present opinions 

 concerning sex-determination are built largely upon the results 

 (chiefly negative) obtained from attempts to control or alter 

 sex, and upon observations on parthenogenetically developing 

 eggs : in part also upon morphological and statistical data. The 

 main object of his paper is to describe attempts to discover by 

 experimental methods, whether the germ-cells have from the 

 beginning a fixed sex-tendency and if so of what kind, and what 

 role fertilization plays in sex-determination. He regards these 

 as fundamental questions which must be answered before one 

 can judge intelligently of the effects of unusual external in- 

 fluences. For the elucidation of these same questions he believes 

 we are largely limited to the plants, particularly the flowering 

 plants, due to the more favorable material they offer for experi- 



In essence, the fertilization process in plants and animals is 

 the same : two germ-cells unite to form a new organism. Botan- 

 ists are to-day convinced of the polyphyletic origin of plants 

 and, while it is possible, it is not very probable that sex-deter- 

 mination and sex-inheritance were arrived at in the different 

 groups by the same path of differentiation. A question to be 

 settled by further work, therefore, is whether the principles 

 determined for the part i < • 1 1 1 ; t v tli>wrrin<_: ['hints under considera- 

 tion apply also to other groups of plants, and also to animals. 



Already in mosses are found a sharply expressed differentia- 

 tion of germ-cells into egg-cells and sperm-cells, and this special- 

 ization is retained with various slight modifications throughout 

 all the higher groups. In phylogenetically lower forms than the 

 mosses the gametes are all alike (swarm spores). Chance or 

 chemotactic influences may bring such into contact and subse- 

 quent union, or they may germinate asexually as in Protosiphon 

 according to Klebs. Externally all are alike. Sometimes, as 

 observed by Klebs in Chlorocytrium, cells from the same mother- 

 cell may copulate. The question arises whether they are in- 

 trinsically alike or whether they consist of two classes, -f- and — , 

 as Blakeslee proposes. In the first case every gamete may copu- 

 late with any other and there is sexuality but no sex-differentia- 

 tion. In the second case only -f and — gametes can copulate 

 and sex-differentiation obtains, the foundation for further dif- 



