26 YiY^SYYT^Cytological Aspect of Parthenogenesis in Insects. 



Von Winiwarter (105) has found that the number is very 

 variable in the rabbit, varyint^ from 36 to 80, the average 

 being about 42. The reduced number in the sexual cells 

 of the rabbit is 12, according to this, then, the somatic 

 number should be 24. Guignard (41) has shown that in 

 certain plants the chromosomes may remain at their reduc- 

 tion number in the somatic cells. Farmer and Shove ('35) 

 have shown that in the somatic cells of Tradescantia the 

 chromosomes vary in number from 26 to 33. There are two 

 varieties of Ascaris, univalens and bivalens, and according 

 to Brauer two types of parthenogenetically developed 

 ArteniicB., possessing 84 and 168 chromosomes respectively. 

 Delage (32, p. 127), who also calls attention to this fact, 

 found in his experiments on fertilising enucleated portions 

 of the ova of Strongyiocentrotus, that the cells of the 

 developing embryo contained 18 chromosomes, although 

 the spermatozoon only contained nine, the reduced number. 

 He also found 18 in the cells of the embryos of the same 

 species which had been made to develop partheno- 

 genetically. All these facts tend to make one believe 

 that there is not an absolute permanency in the number 

 of chromosomes, and favour Delage's view that the 

 number of chromosomes is ' une propriete cellulaire.' 



The suggestion of Stschelkanovzew's (91) raises the 

 further question, to what extent do we get chromatin 

 formed by the change of achromatic material which has 

 entered the nucleus from the cytoplasm ? It is extremely 

 probable that this takes place to a greater extent than is 

 recognised. Cameron (20) has found in studying the 

 development of nerve cells that there is a chromatisation 

 of achromatic material, which he considers as chromatin 

 in a nascent condition. The presence, in some cases, as 

 Alcyoniiim and other Coelenterates, as shown by Hickson, 

 of a large quantity of chromatic material in the cytoplasm 



