236 BIOLOGICAL LECTURES. 



significant morphologically in so far as they Jiave been remodeled 

 by processes of precocious segregation." As regards the spiral 

 cleavage, he believes that it " is a secondary derivative of the 

 true radial type" being the result of " mutual pressure among 

 the cells." Furthermore he says: " But the remarkable fact, 

 and one which does not seem to be very clearly recognized, is 

 that the effect of these mechanical conditions has become hered- 

 itary" And again : " We now come to the main point, which 

 is that the rotation of the cells is in the spiral type in many 

 cases predetermined in the parent cells, as is proved by tJie posi- 

 tion of the spindles and by the form of division" And lastly : 

 "To sum up, I conclude that the spiral form of cleavage is 

 owing to a precocious appearance of the alternation of the 

 cells, which, in its turn, is a result of mutual pressure." 



The question now arises as to the significance of the mutual 

 pressure and the reason for the establishment of the spiral 

 cleavage as hereditary. Discussion along this line must, of 

 course, be of a purely speculative nature, and, although there 

 is a certain truth in Driesch's contention that explanations of 

 this kind do not explain ('99), I still believe that they are of 

 value as showing, perhaps, some of the steps in the process, and 

 a possible or probable motive for these steps, even though the 

 why and the how of the reaction of the organism is a mystery. 



It is clear that the alternation of blastomeres that would 

 result from mutual pressure, etc., produces a form of cleavage 

 in which the blastomeres, like soap bubbles, conform to the law 

 of minimal contact surfaces, and that therefore each blastomere 

 is in contact with the greatest number possible of the others. 

 From the so-called organism standpoint such a relation must 

 unquestionably be advantageous, unless we assume that the 

 peculiar property of protoplasm which binds the cells into an 

 organism is capable of some mysterious "Fernwirkung," which 

 does not seem probable. Roux's " Cytotropismus " appears, 

 perhaps, to be such a " Fernwirkung," but I would like to 

 suggest the possibility that this so-called cytotropism may 

 resolve itself in some cases into the establishment of extremely 

 fine protoplasmic connections. 



From the standpoint of the cell theory this arrangement of 



