306 STUDIES IN GENEKAL PHYSIOLOGY 



for example, such as were ruptured in the sixty-four-cell 

 stage did I usually obtain something different, namely, 

 abnormally formed skeletons. Nevertheless at times I ob- 

 tained under these conditions also real "Siamese" twins. 



4. So far as the theoretical importance of these experi- 

 ments is concerned, the following seems certain : As the burst- 

 ing of the membranes and the flowing out of the protoplasm 

 is a purely mechanical process determined by osmotic forces, 

 no reason is at hand for assuming that qualitatively or quan- 

 titatively the same constituents leave the egg in each case ; 

 according to direct observation, the opposite seems to occur 

 with much more certainty. Nevertheless, the extraovate 

 develops into a complete embryo. It follows from this that 

 every part of the protoplasm can form an embryo. So far 

 as the nucleus is concerned, the two spheres obtain entirely 

 different constituents of the nuclear substance. Nevertheless, 

 they develop in exactly the same way to similar embryos, as 

 Driesch has already shown by other methods. Thirdly, my 

 experiments show that the number of embryos which can 

 arise from an egg is determined by the geometrical form 

 which we give the protoplasm, in so far as each completely 

 or almost isolated sphere (or ellipsoid) of protoplasm deter- 

 mines the formation of a separate blastula, and as the num- 

 ber of blastulse determines the number of embryos. In this 

 way I obtained last year double embryos from a normal egg 

 when I introduced it, in the two-cell stage, into somewhat 

 concentrated sea-water for some time, in which it was unable 

 to segment further. When I brought such eggs back into 

 normal sea-water, each of the two hemispheres broke up into 

 several cells at once. The cells of each of the hemispheres 

 probably adhered to each other, but not to the cells of the 

 other hemisphere, so that an isolation of the two hemispheres 

 was obtained in this way. In one egg I obtained double 

 blastula3. The method deserves to be worked out more care- 



