226 NORMAL HISTOLOGY. 



structure a definite amount of chromatin and a centrosome. During 

 the fertilization of the ovum this chromatin unites with a similar 

 amount present in the egg-cell, and thus forms a complete cell, the 

 nucleus of which contains equal amounts of chromatin from the 

 male and female parents of the future offspring. We have seen 

 (Chapter I.) that the nuclei of the cells throughout the body break 

 up, during karyokinesis, into a definite and constant number of 

 fragments, called " chromosomes," which split during metakinesis ; 

 one-half of each chromosome going to each of the daughter-nuclei. 

 These chromosome-halves form a reticulum within the daughter- 

 nuclei, and Avhile in that form the chromatin appears to increase in 

 amount, so that by the time the cell divides again the full supply 

 of chromatin is present in its nucleus. During the two cell-divis- 

 ions which immediately precede and result in the formation of the 

 spermatozoa and the matured egg this growth of the chromatin 

 does not take place, and, as we shall presently see, each spermato- 

 zoon or matured ovum contains but half of the chromosomes that 

 are normally present in the somatic or general cells of the body. This 

 " reduction of the chromatin " has been a matter of much study 

 within the last few years, because of its probable bearing upon the 

 problems of heredity. The fact of its occurrence is strongly con- 

 firmatory of the idea that the chromatin is the carrier of hereditary 

 characteristics, the fertilized ovum receiving equal shares from both 

 parents. 



The tubular glands of the testis are enclosed in a strong fibrous cap- 

 sule, made up of interlacing bands of fibrous tissue. This becomes con- 

 tinuous, behind, with a mass of areolar tissue containing the vascular 

 supply of the organ and the epididymis, with the vasa efferentia open- 

 ing into it. The fibrous capsule is called the " tunica albuginea." It 

 is covered, except posteriorly, by the visceral portion of a serous mem- 

 brane, the " tunica vaginalis." From the inner surface of the capsule 

 numerous bands and strands of fibrous tissue, trabeculse, traverse the 

 glandular part of the organ, imperfectly dividing it into lobes, each 

 of which contains several of the glandular or seminiferous tubes. 



Upon the surfaces of the trabeculse and upon the inner surface 

 of the capsule the dense fibrous tissue of those structures passes 

 into a delicate areolar tissue, which gives support to the numerous 

 small bloodvessels and abundant lymphatics distributed within the 

 organ. This vascular areolar tissue also penetrates between the 

 seminiferous tubules, giving them support. In this region the 



