ON A SIMPLE METHOD OF PRODUCING FROM ONE 

 EGG TWO OR MORE EMBRYOS WHICH ARE GROWN 

 TOGETHER l 



1. IN the effort to extend my work on heteromorphosis 

 to the embryo, I have discovered a simple method of pro- 

 ducing at will from a single egg two or more embryos which 

 are grown together. My experiments were made on sea- 

 urchins, but it is possible that they can be made with just as 

 great certainty on every other holoblastic egg. Ten minutes 

 after having been artificially fertilized in normal sea-water, 

 eggs of Arbacia were introduced into sea-water to which 

 100 per cent, of its volume of distilled water had been 

 added. The eggs absorbed so much water in the diluted sea- 

 water that their membranes burst and part of their proto- 

 plasm flowed out. The eggs then consisted of two connected 

 spheres of protoplasm (P and P l , Fig. 69), as the extruded 

 drop of protoplasm in consequence of its surface tension 

 assumes a spherical form, as does the protoplasm remaining 

 behind inside the membrane. As segmentation has not yet 

 begun at this time, only one of the two droplets contained a 

 nucleus (Fig. 69). When after some time I returned these 

 eggs into normal sea-water, each of the two spheres of 

 protoplasm developed into an entirely normal and complete 

 embryo. 



In many cases the two embryos remained connected. 

 More often, however, one of the embryos went to pieces in 

 the course of its early development (in about the morula or 

 blastula stage); and finally many double embryos were 

 gradually separated from each other, in consequence of their 



l Pfliigers Archiv, Vol. LV (1894), p. 525. 



303 



