80 PROCEEDINGS OF THE ACADEMY OF [1893. 



•we know to a certainty that there is only one avenue for the access 

 of new material during the process of regeneration of a digit for 

 example, and that is its proximal or basal portion. Through this 

 basal portion alone can new material reach the digit to build up its 

 distal parts. If growth and its accompanying karyokineses were 

 interfered with in any way across a narrow line over the stump, the 

 regenerative energies would be caused to manifest themselves on 

 either side of that line, and the result would be a tendency to repro- 

 duce the digits in duplicate beyond the point of mutilation, and in 

 a divergent fashion from the basal area through which alone new 

 material could find access by intussusception during the process of 

 ■regeneration. We consequently get a mechano-physiological expla- 

 nation of why it is that doubly reproduced distal parts tend to 

 diverge from each other radially. 



The same principle, together with concrescence, may be invoked, 

 as it has been in another form, by Rauber, to explain the degree of 

 fusion of double or triple monsters produced by shaking mesoblastic 

 ova during their early blastodermic stages of development. But 

 Eauber's explanation must in this case be supplemented by a 

 •consideration of the physical laws of the interfacial and free surface- 

 tensions which condition growth during the development of a thin 

 blastoderm in a meroblastic egg, making, for self-evident physical 

 reasons, the production of completely separate embryos well nigh 

 an impossibility, even by shaking or otherwise interfering with 

 development. ' Even if separate germinal disks were developed on 

 a telolecithal egg, there is every reason to believe that, as segmenta- 

 tion proceeded, the two resulting blastoderms would become fused 

 by their edges as the latter advanced over the yolk and approached 

 each other as they necessarily must in order to increase, as they do, 

 in a geometrical ratio, their power of appropriating the stored nutri- 

 tive mass of yolk. On a priori grounds, and for mechanical reasons, 

 therefore, the complete separation of the germinal matter of a 

 large-yolked meroblastic egg is impossible. The total separation of 

 the two first blastomeres of the equally segmenting, holoblastic eggs 

 of echinoderms and Ampluoxus, on the other hand, is easily accom- 

 plished by mere violent mechanical interference, so that completely 

 distinct and separate, but smaller, embryos are easily obtainable 

 if such separated blastomeres are allowed to develop under favorable 

 conditions. 



