OVARIAN ATRESIA AND PARTHENOGENESIS 53 



egg nucleus and cytoplasm, most of which cannot be con- 

 sidered the result of true cleavage processes though in some 

 instances a remarkable resemblance to cleaved ova is at- 

 tained (see Plates IV and V). Another group of investigators 

 generally admit that complex pseudoparthenogenetic frag- 

 mentation occurs, but claim that a varying number of ova 

 enter into true parthenogenetic development (Pfluger, 1863; 

 Flemming, 1885; Paladino, 1887; Lowenthal, 1888; Schott- 

 lander, 1891; Henneguy, 1893; Grusdew, 1896; Rabl, 1898; 

 Gurwitsch, 1900; Spuler, 1900; Van der Stricht, 1901; Loeb, 

 1901, 1905, 1911, a and b, 1912, 1915, 1923, 1932; Newman, 

 1912, 1913; Sansom, 1920; Haggstrom, 1922; Courrier and 

 Oberling, 1923; Courrier, 1923; Branca, 1925; Bosaeus, 

 1926; Lelievre, Peyron and Corsy, 1927). The resolution of 

 such alternative points of view depends first of all upon a 

 clear definition of what parthenogenesis is and secondly upon 

 the interpretation of the ovarian structures designated as 

 embryonic. 



If by parthenogenesis is meant the development of a 

 mature individual from an unfertilized egg then it is at once 

 certain that parthenogenesis does not take place in mamma- 

 lian ovaries. If, on the other hand, a cleavage of the ovum 

 with an equational division of the chromosomes is the cri- 

 terion then there is some evidence (Sansom, 1920; Branca, 

 1925; Engle, 19276) that occasionally parthenogenesis occurs 

 in ovarian eggs (see Plates IV and V). Certainly it is not 

 permissible to consider as parthenogenesis an exact repro- 

 duction of events taking place in the fertilized egg, since it 

 is well known, for example, that parthenogenetic individuals 

 arise from ova in which second polar body formation is 

 suppressed. 



It seems appropriate, in seeking an understanding of the 

 physiological processes occurring in developing eggs, to dis- 

 tinguish between parthenogenesis and activation. A definite 

 series of physical and chemical events ensue in eggs treated 

 by agents inducing parthenogenesis. An apparently iden- 

 tical set of changes occurs at fertilization. This process 



