SEX-CHROMOSOMES AND INHERITANCE 189 



has shown that such kinds of androgenetic embrj^os 

 may arise in the eggs of ChcEtoptencs treated with radium, 

 and by following every stage in the process he has 

 determined also that the embryos have the reduced 

 number of chromosomes. 



Other work on the egg of the sea-urchin had seemed 

 to show that while in most cases the egg, that begins to 

 develop parthenogenetically, starts with, and continues 

 to maintain the half number of chromosomes, yet accord- 

 ing to a recent observation of Brachet, a parthenogenetic 

 tadpole, eighteen days old, that he produced, had the 

 double number of chromosomes. Whether it may turn out 

 that when the egg nucleus gives rise to the nuclei of the 

 parthenogenetic individual it may sometimes double its 

 number of chromosomes (by failure of the first cytoplas- 

 mic division, for example), and that when a sperm gives 

 rise to these nuclei the half number is retained, cannot be 

 stated. Until we have farther information on these points 

 the expectation as to what the sex of parthenogenetically 

 produced frog individuals will be can only be speculative. 

 Loeb has raised seventeen adult, or nearly adult male 

 frogs and three nearly adult female frogs from eggs devel- 

 oping after Bataillon's puncture method of inducing par- 

 thenogenesis. One male frog had more than the half num- 

 ber of chromosomes (at least 20 and presumably the 

 whole number, 261). The number of chromosomes in the 

 females was not determined. 



Gynandeomorphs and Sex 

 In the group of insects especially, it has long been 

 known that individuals occasionally appear that are part 

 male, part female. In the most striking cases the line 

 of division runs down the middle of the body, but there 

 are also antero-posterior gynandromorphs, and individ- 

 uals with only a quadrant or even a small piece of the body 

 different from the rest in its sex character. Several 

 hypotheses have been advanced to explain these rare com- 



