1890.] 151 [Ryder< 



division of labor observed. This process of morphological specialization 

 in Volvox is therefore not necessarily due to natural selection alone. 



There are still other reasons why the physiological specializations in 

 Voloox have proceeded along the lines they have. It may be asked why 

 the germ-cells tend to bulge inwards as they enlarge into the jelly which 

 fills the cavity of the colonial sphere. Why do they not bulge outwards ?- 



To this it may be replied that light, oxygen and food react from the ex- 

 terior of the colony. The mobile protoplasm through which supplies of 

 nutriment come, must be most exterior. The katabolic running down of 

 the accumulated nutriment matters into less mobile coarse granules which 

 need and consume less oxygen, requires that these materials shall be 

 pushed inwards where they will not obstruct respiration. 



In this way, upon the ground of physiological anatomy and the reaction 

 of the incident surrounding forces, the process of the "setting aside of 

 the germ-plasma " in Volvox can be fully accounted for without appealing 

 for an instant to natural selection. There is clearly nothing further 

 needed. 



It might be said that " natural selection " would favor only those indi- 

 viduals which did not have the germ-cells bulging outwards, because they 

 could not so conveniently rotate or move forwards. Yes, but Volvox does 

 not, in the first place, continuously rotate. In the next place, even if 

 "natural selection " did work the wonders claimed for it, it is clear that 

 the explanation here suggested is one which involves no waste of the 

 forces of growth or of individuals, but is operative in virtue of the con- 

 tinuity of the processes of growth, besides it meets the requirements 

 equally well with the hypothesis of natural selection. 



The natural selectionist will next appeal to the morphology of Volvox in 

 some other direction and ask, How was the hollow sphere evolved ? This, 

 in its turn, is clearly and purely adaptive. The growth of the original 

 colonies, which were doubtless evolved from such as broke down into 

 planogametes, grew directly into larger multicellular aggregates which 

 would directly arrange their cells so as to derive the greatest advantage 

 from the surroundings and in attaining that adjustment, the globular form 

 was assumed, in that it offered the maximum opportunity for oxygen, 

 food, etc., in the form of a hollow sphere with the gametes joined by pro- 

 toplasmic bonds. The selection of the pattern of the form of the whole 

 organism is thus traced to internal forces acting in direct response to outer 

 conditions and not as the result of a murderous process of "selection" 

 and " survival of the fittest." * 



But this is not all, if the argument applied to the driving inward of the 



*The method of segmentation itself must be regarded as a necessary adjustment of 

 the cleavage planes in such wise, as to divide the large globular ovi-cells into approxi- 

 mately equal parts continuously. An adjustment of this sort effects the equal reduction 

 of all the cells resulting from segmentation, and keeps them below a dimension or mass 

 which outruns the surface to an extreme degree, since according to the Leuckart-Spencer 

 principle beyond a dimension of six, mass begins to rapidly exceed surface and bring 

 about conditions unfavorable for respiration and metabolism. 



