452 HISTOLOGY 



duction of a male. This fact is admirably illustrated in the above 

 diagram by Wilson (Fig. 415). Modifying Wilson's formula for sex 

 production, to cover the case of Aplopus, the whole theory with facts and 

 assumptions may be succinctly stated as follows : 



I. ? Egg (18 chromosomes) + ( $ ) sperm (18 chromosomes) = 

 $ ( $ ) female (36 chromosomes). 



II. $ Egg (18 chromosomes) + (o) sperm (17 chromosomes) = 

 ( $ ) (o) male (35 chromosomes). 



Technic. Owing to the lack of yolk, and to the uniform protoplas- 

 mic texture of the specific male reproductive tissues, the technic has been 

 easy, requiring only great care and exactness and a reasonable apprecia- 

 tion of the element of luck, represented by the unknown, and sometimes 

 unmeasurable, factors which unite to make a successful or unsuccessful 

 preparation. The various osmic and chromic fixatives, particularly 

 Flemming's strong mixture and Hermann's fluid, have perhaps been 

 most used, and with the greatest success. Corrosive sublimate and 

 Zenker's fluid have been very successful in many cases. Smear prepara- 

 tions have been used in a few cases and ought, if used carefully, to be 

 superior as a means of merely counting well separated and compact 

 chromosomes. They cannot be trusted to show the relations of parts. 

 The earlier stages of spermatogenesis have been observed during life by 

 Wilson in the case of Anasa. 



LITERATURE 



From a very large list of good papers we will select only a few in which more complete 

 bibliographies may be found. 

 WILSON, E. B. "Studies on Chromosomes" in the Journ. of Experimental Zool., Part I 



in Vol. II, 1905, p. 371; Part II in Vol. II, 1905, p. 371; Part III in Vol. Ill, 1906. 



The sexual differences of the chromosome groups in Hemiptera, with some con- 

 siderations of the determination and inheritance of sex. 

 BRATJER, A. "Zur Kentniss der Spermatogenese von Ascaris megalocephala," Arch. f. 



mik. Anat., Band XLII, 1893. 

 MEVES, F. " Uber die Entwicklung der mannlichen Geschlechtszellen von Salamandra 



maculosa," Arch. f. mik. Anat., Band XLVIII, 1896. 

 MOORE, J. E. S. "On the Structural Changes in the Reproductive Cells during the 



Spermatogenesis of Elasmobranchs," Quart. Journ. Micr. Sci., Vol. XXXVII, 1895. 

 PAULMIER, F. C. "The Spermatogenesis of Anasa tristis," Journ. of M or ph., Vol. XV, 



Supplement. 

 McCLUNG, C. E. "The Accessory Chromosome Sex-Determinant," Biol. Bull., Vol. Ill, 



Nos. i and 2, 1902. 

 STEVENS, N. M. "Studies in Spermatogenesis n." A comparative study of the hetero- 



chromosomes in certain species of Coleoptera, Hemiptera, and Lepidoptera with 



special reference to sex determination. Carnegie Inst. Wash. Pub., Vol. XXXVI, 



No. 2, 1906. 

 CASTLE, W. E. " The Heredity of Sex," Bull. Mus. Comp. Zool., Harvard, Vol. XL, No. 4, 



1903. 



SUTTON, W. S. "The Chromosomes in Heredity," Biol. Bull., Vol. IV, No. 5, 1903. 

 JORDAN, H. E. "The Spermatogenesis of Aplopus Mayeri," Carnegie Inst. of Wash., 



Pub. No. 102, 1908. 



