io8 POPULAR SCIENCE MONTHLY. 



to the contrary, for in the great majority of forms all the spermatozoa 

 that are formed develop in the same way and are, so far as we can see,, 

 capable of fertilizing the eggs.* 



Beard's conclusions in regard to the determination of sex may be 

 summarized as follows: 



1. The sex of the individual is determined in the egg before fertil- 

 ization. 



2. The determination of sex probably takes place at the time of 

 the reduction in the number of chromosomes. 



3. Each egg and its two polar bodies are potentially of the same 

 sex, either male or female. 



4. A corresponding differentiation of the primary germ-cells takes 

 place in the male. An early separation of the spermatogonial cells 

 into male and female occurs. After this each cell may continue to 

 divide, but remains of the sex that it has acquired in the differentiating 

 division. Finally each of these cells produces four spermatozoa. This 

 division is comparable to the one in the egg-series when the polar 

 bodies are given off, so that each group of four spermatozoa corre- 

 sponds to a female egg and its three female polar bodies, or to a male 

 egg and its three male polar bodies ; but in the cases of the spermatozoa 

 the individuals are supposed to be without sexual qualities. It is the- 

 egg alone that determines the sex. 



5. One set of these fourfold groups of spermatozoa Beard sup- 

 poses to have become functionless, in the sense that even if it develops 

 the spermatozoa have lost the power to fertilize the eggs. The other 

 spermatozoa are functional so far as fertilizing the egg is involved, but, 

 as stated above, take no part in the determination of sex. 



Beard also advances certain views in regard to parthenogenesis. 

 The sex of the individual that develops from a non-fertilized; i. e., 

 from a parthenogenetic egg, is not in any sense a consequence of the 

 non-fertilization of the egg. Whether the individual is a male or a 

 female depends entirely upon whether a male or a female egg has been 

 produced. Whenever we find long series of parthenogenetic females, 

 as in the aphids, developing from and also producing parthenogenetic 

 eggs, Beard supposes that only female eggs have been produced in the 

 ovary, and that the male eggs, which have appeared in one at least of 

 the first generations of the germ-cells 'must be either delayed in their 

 ripening or suppressed.' Here we meet with a paradox that is so 



* Meves has recently found in a male bee that two kinds of spermatids are 

 formed by an unequal division of the spermatocyte. The smaller of the two, 

 although it begins to undergo changes similar to those which in the larger 

 one produce a spermatid, appears to be arrested in its development before 

 the change is completed. Mittheilungeti Verein Schlesw.-Holst. Aerzte, XI., 

 Mai, 1903. 



