THE BIOLOGY OF THE CELL SURFACE 



larval stage of those eggs whose induced parthenogenetic 

 development has not been followed farther. 



After successful treatment with a parthenogenetic means 

 eggs whose optimum period for fertilization follows com- 

 plete maturation develop parthenogenetically with one set 

 of chromosomes (example: echinids). The egg of the frog 

 after puncture (the method used for inducing partheno- 

 genesis in this egg) made after extrusion of the first polar 

 body, which is the fertilizable stage for this egg, extrudes 

 the second polar body and begins development always with 

 only a single garniture of chromosomes, while in later devel- 

 opment this chromosome-number has been found doubled. 

 The situation is different with eggs physiologically ripe for 

 fertilization in either the stage of the intact germinal vesicle 

 or that of first maturation. After successful treatment 

 with a means of experimental parthenogenesis, they develop 

 with or without one or both polar bodies — hence, their 

 blastomeres contain single, double or more garnitures of 

 chromosomes. 



It is thus clear that development induced by experimental 

 means does not depend upon the presence of two or more 

 sets of chromosomes. In this respect experimental par- 

 thenogenesis resembles the normal. An explanation of 

 either type of development can not, therefore, be based 

 upon a bipartite make-up of the first cleavage-nucleus. 

 Here we note, however, the following difference between 

 the natural and the experimental process: in natural par- 

 thenogenesis the egg always has the nuclei of both polar 

 bodies available although it develops with or without the 

 union of the second of these with the definite egg-nucleus. 

 In experimental parthenogenesis the polar-body nuclei are 

 not always available for fusion with the egg-nucleus. This 

 difi"erence is due to the fact that in eggs which possess the 

 capacity for natural parthenogenesis, development, either 

 with or without spermatozoon, begins in the stage of first 

 maturation, i.e., before polar body extrusion — whilst eggs 



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