THE MICROCOSM OF THE EGG 141 



Another kind of experiment shows that a half or 

 less may be as good as a whole. By delicate meth- 

 ods of microscopic vivisection, Professor Delage 

 was able to cut off non-nucleated fragments from 

 a sea-urchin ovum. They accepted fertilization, 

 however, and developed into embryos. In many 

 cases, when a fertilized egg-cell has divided into two 

 cells, these can be shaken apart with the result 

 that each develops into an entire animal. If in the 

 two-cell stage of the developing frog ovum, one cell 

 be punctured with a heated electric needle, the 

 remaining cell will develop into a one-sided hemi- 

 embryo or into a half-sized whole embryo, accord- 

 ing as the punctured ovum is kept fixed or allowed 

 to move (and readjust itself) in the water. Indeed, 

 if a part of an ovum or of a developing ovum is to 

 serve as the equivalent of a whole, the essential 

 condition seems to be a restoration of the typical 

 topography and a re-establishment of the pro- 

 portions of materials. If a vessel of sea-water con- 

 taining developing eggs of the lancelet be shaken 

 at the two-cell stage, the result, according to the 

 amount of shaking, will be a double supply of dwarf 

 embryos, or a set of Siamese twins. Even at the 

 four-cell stage, the shaking will result in numerous 

 dwarf embryos, or in queer Siamese triplets and 

 quadruplets. Perhaps, however, we have said 

 enough to suggest the wonder of the egg-cell, and to 

 make this certainty clear, that no easy-going view 

 of the microcosm is in the direction of the truth. 



