HAPLOIDS Itl 



in, it divides the same number of times as does the normal 

 egg, each of its cells will be in proportion to its chromo- 

 some number twice as large as the normal cells in propor- 

 tion to their chromosome number. In so far as the de- 

 velopment of the cell is dependent on its genes there may 

 be an insufficiency of gene material to produce a normal 

 effect on a cytoplasm of double volume. 



On the other hand, if such an egg should pass through 

 one more division than does the normal egg before dif- 

 ferentiation (organ formation) begins, the number of 

 chromosomes (the nuclear size) would then be propor- 

 tionate to the cell size — there would be twice as manv 

 cells, and twice as many nuclei in the whole embryo as 

 in the normal. The embryo as a whole would then contain 

 the same total number of chromosomes as does the nor- 

 mal embrvo. How far the smaller size of the cells in such 

 a case might affect the developmental process we do not 

 know at present. Observation of the cell-size of haplonts 

 seems to show that the cells have the normal size and that 

 the nuclei are only half as large as the normal ones. It 

 appears, then, that the embryo does not rectify its nu- 

 clear cytoplasmic relation as just indicated. 



It might be possible in another way to determine 

 whether the weakness of the artificial haplonts is due to 

 an insufficiencv of genes for cells as larp-e as normal ones. 

 Half of an egg, containing a single sperm nucleus, would, 

 if it passed through the number of divisions characteris- 

 tic of the normal egg, be made up of cells and nuclei hav- 

 ing the normal size-ratio to each other. Sea urchin em- 

 bryos of this kind have, in fact, long been known. They 

 become plutei that appear to be normal, but none have 

 been carried beyond the pluteus stage because, for one 

 reason, it is difficult to carry even normal embryos fur- 

 ther than this stage under artificial conditions. It is not 

 certain, therefore, whether these haplonts are as viable 



