Ryder.] [May 16, 



The causes of the "setting aside" of the "germ -plasma have acted 

 directly and in an adaptive manner." "Nature is no spendthrift but takes 

 the shortest way to her ends." Weismann assumes that the reproductive 

 cells are "set aside" as the consequence of the action of the principle of 

 the physiological division of labor. The cause of the physiological divi- 

 sion of labor he attributes to the " action" of "natural selection." Is 

 this true ? 



Taking one of the lowest forms of reproductive activity as illustrated in 

 Volvox we find that the germ-cells are not yet constantly or definitely 

 localized except that we may say that they arise in the posterior hemi- 

 sphere of the colony. Examining Volvox from the standpoint which recent 

 knowledge has afforded, it is clear that the anterior pole is differentiated 

 to a degree not attained by the posterior pole. This differentiation clearly 

 stands in a definite relation to the greater action of the light on the anterior 

 pole from the germinal condition onwards through life. It also stands in 

 a definite relation to the differentiation of the anterior pole as the directive 

 and phototaxic one in the course of the execution of the motions of the 

 whole organism rotating on a definite axis. 



Furthermore, the organism when at rest, as it frequently is at the sur- 

 face of the water, has the upper pole turned towards the light, and under 

 these circumstances is it not to be supposed that the lower pole, which is 

 the heavier on account of the presence of the large germs, would gravi- 

 tate into its inferior position ? I do not see how such an admission is to be 

 avoided. If this is so the tendency once begun would tend to be intensi- 

 fied, since those peripheral cells which began to be receptive to the surplus 

 nutriment elaborated by the whole organism would tend to maintain that 

 tendency and the heavier they grew the more constantly they would tend 

 to turn the anterior pole, where the largest " eye spots " are found upward 

 towards the light. This would give the light an opportunity to maintain 

 the specialization of the anterior pole as the photophilous one, and thus 

 intensify its phototaxic tendencies. 



The anterior pole would then be most active in its reactions to light, the 

 posterior one least so as is actually the case. The evolution of the physio- 

 logical differentiation of Volvox can therefore be directly traced to the 

 action of the principle of overgrowth or overnutrition reacting under the 

 influence of gravity upon the equilibrium of the colony so to adjust it that 

 the colony will be uniformly acted upon generation after generation in the 

 same way upon the upper pole. This would be an all-sufficient cause of 

 the physiological differentiation or the real cause of the physiological 



mixed together. Balbiani has obtained somewhat similar results with the testes of 

 Elasmobranchs and Mammals, using picrocarmine and methyl green. If the polar cells 

 are abortive male elements they should have a greater affinity for methyl green than the 

 female pronucleus. If such results were secured my hypothesis would obtain micro- 

 chemical verification. Indeed, I am inclined to think that the fact which I have 

 observed, that the one pole of the dumb-bell-shaped chromatin mass in the nucleus of 

 the immature egg of Ostrea stains with methyl green, while the other pole stains with 

 saffranin is distinctly in favor of my interpretation. 



