SPERMATOGENESIS— INSEMINATION 163 



inside of the spermatocytes, are the double products of division of 

 the latter. The spermatids so formed may be seen as small cells 

 with spherical nuclei, and forming irregular clumps on the inner 

 surface of the tubule. Often, however, the spermatids are elongated, 

 being partially converted into spermatozoa. As this process of 

 transformation proceeds, the developing sperms become arranged in 

 little groups. Associated with each group is a foot-cell, or a cell 

 of Sertoli, which probably serves as a support and as a means of 

 conveying nourishment to the growing spermatozoa.^ The tails of 

 the latter at this stage project freely into the cavity of the tubule, 

 and a little later the spermatozoa shift bodily forward and become 

 completely liberated. According to Loisel,^ the orientation of the 

 sperms in the testis is due to a secretion from the cells of Sertoli, 

 ■ together with certain of the other cells in the parietal layer of the 

 seminiferous epithelium. 



Fig. 49. — A cell of Sertoli with which the spermatids (three of which are 

 shown) are beginning to be connected — human. (After Bramman, from 

 Schafer.) The cell contains globules of nutritive substance, and similar 

 smaller globules are seen in the spermatids. 



In male animals which have a rutting season spermatogenesis 

 occurs only at this time. At other seasons of the year the testes 

 remain in a quiescent condition. The periodic activity of the testis 

 is usually correlated with a great increase in the size of that organ 

 (see pp. 22 and 55). In the hedgehog the interstitial cells have 

 been shown to proliferate even more than the spermatogenetic tissue, 

 the seminiferous tubules becoming widely separated.^ The same fact 

 has been observed in the woodchuck * after hibernation, and in the 

 spring and summer. As with the hedgehog the interstitial hyper- 

 trophy is followed by regression with the approach of autumn. 



1 Merkel, "Die Stiitzzellen des Menschlichen Hodens,'' MiiUer's Archiv, 1871. 

 Brown, " On Spermatogenesis in the Eat," Qtiar. Jov/r. Micr. Science, vol. xxv., 

 1885. Bende, " Untersuchungen iiber den Bau und Funktioniren des Samen- 

 kanalchens einiger Saugethiere," Arch. f. Mikr. Anat., vol. xxx., 1887. 



2 Loisel, " Facteurs de la Forme et de la Fascieulisation des Spermies dans 

 les Testicules," Jour, de I'Anai. et de la Phys., vol. xlii., 1906. 



3 Marshall, "The Male Generative Cycle in the Hedgehog," Jour, of Physiol., 

 vol. xliii., 1911. Similar changes occur in the mole. See Tandler and Gross, 

 Die Biologischen Grundlagen der Sehmddren Oeschlechtscharaktere, Berlin, 1913. 



* Easmussen, " Seasonal Changes in the Interstitial Cells of the Testis in the 

 "Woodchuck," Amer. Jour, of Anat., vol. xxii., 1917. 



