672 THE PHYSIOLOGY OF REPRODUCTION 



the sex chromosome ^ passing into the polar body ; at a temperature of 

 35° to 37° C, however, fewer females appear (ratio 62 ? to 100 S). 

 This work has been well reviewed by Goldschmidt.^ 



It has been known for a long time that two kinds of sperm exist 

 in the snail Paludina, a hair-like form and a worm-like form, but it 

 is commonly believed that only the former is functional. Dimorphic 

 spermatozoa have also been discovered in various other animals, but 

 the differences between the two kinds vary greatly.^ 



Henking* made the discovery that in the bug, Pyrrhocaris, half 

 of the spermatozoa differ from the other half in possessing an 

 additional chromosome. M'Clung ^ was the first to suggest that the 

 difference between tlie two sorts of spermatozoa in this insect was 

 connected with sex-determination, and that those which contained 

 the accessory chromosome produced males, and that those without it 

 produced females. The last assumption has, however, proved to be 

 incorrect, since Wilson'^ found that in this and other forms the 

 female and not th& male contains an additional chromosome in its 

 somatic cells. It is almost certain also that the ova have one more 

 chromosome than one half of the sperms have, and the same number 

 as that possessed by the sperms which contain the additional chromo- 

 some. Consequently the latter are supposed to produce females, and 

 the former males. 



For example, in Anasa tristis the somatic cells of the male contain 

 twenty-one chromosomes, whereas those of the female contain'twenty- 

 two. Half of the spermatozoa are supposed to contain eleven 

 chromosomes, the other half having only ten. The ova are believed 

 to all resemble one another in containing eleven chromosomes. It is 

 concluded, therefore, that the spermatozoa possessing the smaller 

 number give rise to males, while those with eleven chromosomes 

 produce females.^ 



1 See below, p. 673. 



^ Goldsclimidt (E.), Mechanismus und Physiologie der Geschlechtshestimmung, 

 Berlin, 1920. 



^ A list of species in which dimorphic forms of spermatozoa have been 

 recorded (down to 1902) is given by Beard, loc. cit. 



* Henking, " Untersuchungen ueber die ersten Entwicklungsvorgange in 

 den Eien der Insekten," ZeiUch.f. wiss. ZooL, vol. xlix., 1890, and vol. li., 1891. 



^ M'Clung, "The Accessory Chromosome Sex Determinant," Biol. Bull., 

 vol. iii., 1902. 



^ Wilson (E. B.), " Studies on Chromosomes," Jour, of Exp. ZooL, vols. ii. 

 and iii., 1905-06 ; vol. vi., 1909. " Note on the Chromosome Groups of Metapodius 

 and Banusa," Biol. Bull., vol. xii., 1907. " The Supernumerary Chromosomes of 

 Hemiptera," Science, vol. xxvi., 1907. See also Stevens, " Studies in Spermato- 

 genesis," Part I., 1905, and Part II.,- 1906, Carnegie Institution (Washington) 

 Publications. In these papers dimorphic spermatozoa (one kind containing 

 one smaller chromosome or lacking one chromosome) are described for various 

 species of Orthoptera, Coleoptera, Hemiptera, and Lepidoptera. 



' Foote and Strobell ("A Study of Chromosomes in the Spermatogenesis 

 of Awxsa tristis,'' Amer. Jour, of Anat., vol. vii., 1907), as a result of an investiga- 



