28 J. E. WODSEDALEK. 



these long-continued searches, accurate counts of chromosomes 

 in the cells of the various tissues were comparatively few. How- 

 ever, all cases where a count was possible were recorded and 

 although they varied somewhat, the above number of chromo- 

 somes, eighteen and twenty, attributed to the male and female 

 cells respectively, were the prevailing numbers. 



The foregoing facts are in accord with the expectations, and 

 we have here in a vertebrate a condition verifying the results 

 found in some of the lower forms. In view of these facts it is 

 obvious that the eggs, carrying ten chromosomes, or half the 

 somatic number, when fertilized by a spermatozoan containing 

 ten chromosomes, give rise to an individual containing twenty 

 chromosomes in its -cells, or a female. Those fertilized by the 

 other type of spermatozoan, which contains only eight chromo- 

 somes, give rise to individuals with eighteen chromosomes in their 

 cells, which was found to be true in the male. 



The results of the present investigation, therefore, add support 

 to the chromosome theory of sex determination, since they show 

 that in the vertebrates, as well as in some of the lower forms, 

 there exists a dimorphism in the number of chromosomes in the 

 somatic as well as the germinal cells of the two sexes. It is 

 highly probable that conditions similar to those found in the pig, 

 as regards sex determination, exist in man and in the other 

 vertebrates which possess the accessory or X-chromosomes. The 

 resemblance in the behavior of the pair of accessories in the pig 

 and their behavior in man is very striking and suggests that in 

 all probabilities there exists a dimorphism in the germinal and 

 somatic cells of man and woman. 



SUMMARY. 



1. The usual four types of cells, the spermatogonia, primary 

 and secondary spermatocytes, and spermatids are discernible in 

 the spermatogenesis of the pig. 



2. Large interstitial cells containing numerous mitochondria 

 exist in great abundance and comprise about one fourth of the 

 entire mass of the testes. 



3. Numerous Sertoli or nurse cells are present and great 

 numbers of spermatozoa can be seen in all stages of development 

 in the various tubules. 



