Artificial Partlnniogenesis m Thalasseiua Mellita 



III 



In the living parthenogenetic egg, the polar bodies are abso- 

 lutely indistinguishable in position, size, form and other character- 

 istics from those formed after fertilization by sperm. Conn ('86) 

 described the almost invariable division of the first polar body, 

 but as his observations were limited nearly entirely to the living 

 ^gg-, he did not follow the details of the mitotic phenomena. 

 Griffin ('99), however, from a careful study of sections, determined 

 that the first polar body divides by a complete and typical mitosis, 

 although in certain minor details there are signs of degeneration. 

 The same mitotic phenomena and division occur almost without 

 exception in the parthenogenetic eggs, and will be described be- 

 yond. Fig. 4, showing the divided first polar body, is drawn 

 from a living egg which had been exposed to the action of acetic 

 acid; the first polar body in this case appeared in 45 minutes 

 after removal from the solution, and the second 15 minutes later. 



It is of interest to note that the polar bodies respond to the same 

 divisional stimulus supplied by the acid solutions as does the egg 

 cell itself, as both bodies have been frequently seen to undergo 

 several cleavages. This revived activity of the degenerate polar 

 cells, which may be regarded as an abortive parthenogenesis, results 

 in the formation of a miniature, morula-like cluster of minute cells 

 which, however, soon break away in a mass from the surface of 

 the egg and may persist for some time in the space beneath the 

 membrane. Exposure to the acid solutions restores to a certain 

 degree the energy of division in these rudimentary germ cells and 

 an attempt at development follows. As many as sixteen cells 

 have been counted with certainty in the miniature embryos, and, 

 although I have not been able to determine it in all cases, it is 

 certainly true that some at least of these subsequent cleavages of the 

 polar cells take place mitotically. In Fig. i is seen an instance in 

 which at least ten cells have been formed, and Fig. 62 is drawn 

 from a section which has passed through five cells of a cluster; 

 two of these show indications of mitotic activity. 



This parthenogenetic development of the polar bodies in 

 Thalassema should be compared with the observations of Fran- 

 cotte ('97) on a turbellarian, Prostheceraeus; here the first polar 



