Beard, Heredity and the epicycle of the gerni-cells. 



403 



possible, that at present the embryo would be found to arise in any 

 case from such a spore-mother-cell. Only its formation at some time 

 in the past from a spore-mother-cell was spoken of, because the facts 

 of development at that time known seemed to point to its origin from 

 at least a few cells. 



And, moreover, everything then seemed to go to prove the pro- 

 duction of the ,,sexual organs", i. e., the germ-cells, by the embryo 

 itself. Such was the belief of almost every embryologist, and there 

 appeared little or no reason for doubting its correctness. 



Revised Comparison of Metazoan and Metaphytic 



Life-Cycles. 



Metazoon. Metaphyte. 



zygote (2n) zygote (2n) 



I I 



n larva" or phorozoon (2 n) sporophyte (2 n) 



> 



CO 



en? 



a 



B 



a> 

 t 

 P 

 -*- 



o* 



B 



| I 



formation of primitive germ-cell (2n) formation of primitive spore-mother- 

 cell (2 n) 



formation of primary germ-cells (2 n) formation of spore-mother-cells (2 n), 



probable determination of sex and 

 reduction 



n apospory" (reduction postponed) 

 / primary germ-cells (2n) 



spore-formation 



CD 



X 



a 

 o> 

 >t 



fa 



<rt 



5' 



B 



spores (In) 



(Initiation of Determination of Sex) origin of gametophyte from one 

 origin of embryo or gametozoon spore (1 n) 

 from one primary germ-cell, in- 

 clusion of rest in gametozoon (2 n) 



End of determination of sex, and ripening of germ-colls, reduction 

 reduction of chromosomes, ri- previously effected 

 pening of germ-cells 



spermatozoon (1 n) egg (1 n) 



zygote (2n) 



male female 



gamete (1 n) gamete (1 n) 



zygote (2n) 



The effect of these two factors was to bar further progress in 

 that direction, at any rate for a time. In face of the apparent facts, 

 I confess, that it was impossible to foresee how the formation of the 

 spore-mother-cell was effected, with the natural result, that only its 

 former existence, i. e., in past times, was suggested. Moreover, there 

 was not the slightest suspicion in my mind or Murray's that the 

 germ-cells had anything to do with the matter. 



It is possibly a humiliating confession to make, but it is quite 

 true, that I was never able to conceive how Nature could carry out 



26* 



