1 88 DYNAMICS OF LIVING MATTER 



which copulate. As in Aphides, only a definite type of eggs, the so- 

 called winter eggs, require fertilization, and from the fertilized eggs a 

 female originates in every case. In Rotifers also the winter eggs are 

 said to require fertilization and give rise to females. 



We have already mentioned the fact that in bees the unfertilized 

 eggs give rise almost, or quite exclusively to males, while females 

 can only (or perhaps mainly) arise from fertilized eggs. This seems to 

 indicate that the entrance of a spermatozoon may give the egg a female 

 character, while without it, it has a male character. Lenhossek believes 

 it is possible that in bees, as perhaps in most animals, two kinds of eggs 

 exist, one for each sex ; that for some reason the male egg is not fertilized 

 when it is laid, while the female is fertilized. It is, however, difficult 

 to harmonize with such a view the fact that old queens, whose supply of 

 sperm in the receptacle is exhausted, and virgin queens lay only male 

 eggs. 



Among certain insects, e.g. the Hemiptera and Orthoptera, two' 

 kinds of spermatozoa have been found, but one kind of eggs. These 

 two kinds of spermatozoa differ in regard to a single chromosome, which 

 is found only in one half of the spermatozoa, while it is lacking in the 

 other; or which is larger in one half of the spermatozoa than in the 

 other half. 



The first one to recognize the existence of two kinds of spermatozoa 

 was Henking, who stated that in Pyrrhocoris (a Hemipteron) one half 

 of the spermatozoa of each male possessed a nucleolus while the 

 other half did not. Montgomery afterwards showed that Henking's 

 nucleolus was an accessory chromosome. To McClung * of the Uni- 

 versity of Kansas belongs the credit of having first recognized the 

 importance of this fact for the problem of sex determination. He 

 observed an accessory chromosome in one half of the spermatozoa of 

 two forms of Orthoptera, Brachystola and Hippiscus, and traced their 

 history. His conclusion may be quoted in full: "A most significant 

 fact, and one upon which almost all investigators are united in opinion, 

 is that the element is apportioned to but one half of the spermatozoa. 

 Assuming it to be true that the chromatin is the important part of the 

 cell in the matter of heredity, then it follows that we have two kinds 

 of spermatozoa that differ from each other in a vital matter. We 

 expect, therefore, to find in the offspring two sorts of individuals in 

 approximately equal numbers, under normal conditions, that exhibit 

 marked differences in structure. A careful consideration will suggest' 

 that nothing but sexual characters thus divides the members of a species 



* C. E. McClung. The Accessory Chromosome Sex Determinant ? Biological Bul- 

 letin, Vol. 3, p. 43, 1902. 



