74 SCIENCE PROGRESS 



this latter case the number of chromosomes doubles during 

 the later stages of development, a female might be expected 

 to arise. 



But how can one explain the two-sex production of the 

 frog ? Unfortunately, the cytological investigations on Am- 

 phibian eggs are very few, and even these are contradictory. 

 Thus, in 191 3, Herlandt^ stated that, after pricking the eggs 

 with a glass rod, the second maturation division was completed, 

 leaving the pro-nucleus haploid. This was asserted earlier 

 by Dehorne, who, however, believed that during the subsequent 

 development of the egg the diploid condition was re-established 

 by division of the chromosomes (auto-regulation). Brachet 

 found the diploid number of chromosomes in the somatic cells 

 of an eighteen-day-old tadpole, raised by means of artificial 

 parthenogenesis, but did not determine the chromosome number 

 before segmentation of the egg. According to Swingle * the 

 diploid chromosome number is 26. The latest observations 

 we owe to Loeb and Parmenter'; the former, in conjunction 

 with R. Goldschmidt, counted the chromosomes in the testes 

 of one fully developed parthenogenetic frog seventeen months 

 old. Ripe spermatozoa were seen, and over twenty chromo- 

 somes found in the developing cells, thus making it probable 

 that in this frog the condition was diploid, Parmenter 

 investigated more fully Loeb's material, and found the diploid 

 condition in three adult males and thirteen tadpoles. Some 

 of the cells were undergoing maturation, and the tetrads, clearly 

 haploid in number, appeared of the same form as in normal 

 material. Unfortunately, the chromosome number in partheno- 

 genetic female frogs has not yet been determined. As Herlant 

 has shown, the nucleus of the egg immediately after treatment 

 is haploid ; the subsequent diploid condition, therefore, must 

 arise by division of the chromosomes without division of the 

 cell body, or by retention of the second polar body, which, 

 according to Herlant, is not the case. Hence, one must conclude 

 that auto-regulation occurs. It should be mentioned, in passing, 

 that, according to Nachtsheim, this is a normal phenomenon 

 in the somatic cells of male Hymenoptera. 



Having reviewed the chief cytological investigations on the 

 parthenogenetic eggs of frogs, the question may be asked, What 

 light do they throw on sex-production ? It must be conceded 

 at once that no clear-cut statement can be made, especially 

 in view of the fact that at present it is undetermined as to 

 whether the normal frog possesses sex-chromosomes or not. 



iHerlandt, M., Arch.de Biol., 28, 1913 ; C. R., Ac. des Sci. 158,164; 1914, 

 1917 ; Bull. Scientif., 50, 1917 ; Arch. Zool. Exp. et Gen., 57, 58 ; 1918, 1919. 



2 Swingle, W. W., Biol. Bull., 33, 1917, p. 70. 



3 Parmenter, C, L., Journ. Gen. Physiol., 2, 1920, p. 205. 



