THE MALE ORGANS OF GENERATION. 237 



lumen of the tubule, are the seminal cells of Sertoli. These 

 latter are usually arranged in two or more layers, polyhedral 

 in shape when placed closely together, but more spherical when 

 next to the lumen of the tubule ; they are uniform in size and 

 contain a single nucleus. The nucleus is spherical, possesses 

 no limiting membrane, and contains a convolution of thick 

 fibrils, or rods, in a transparent matrix. A more minute ex- 

 amination of the nucleus shows that the fibrils are arranged in 

 certain definite forms, which indicate changes preparatory to 

 division, as has been pointed out by Strassburger, Hertwig, 

 Flemming, and others. The various forms, taken by the nucleus 

 before dividing, correspond to what is termed the "convolu- 

 tion," the "basket," the "wreath," the "monaster," or the 

 " dyaster." The entire process of the indirect division of the 

 nucleus is termed by Flemming TcaryoJcinesis. 



Toward the lumen of the tube the above-described cells are 

 seen with their nucleus either dividing or divided into two 

 daugliter -nuclei. From these daughter-nuclei are developed 

 the daughter-cells, or spermatoblasts, and by an interesting 

 series of changes the spermatozoa are formed. 



"The nucleus of the spermatoblasts at first retains its spher- 

 ical shape, but is invested in a distinct membrane, the convo- 

 lution of fibrils changes into a honey-combed reticulum, some- 

 times with one or two nucleoli, and the nucleus is not placed 

 in the centre but in the periphery of the cell." 



" Next the nucleus becomes uniform in its substance and 

 transparent, all traces of a reticulum have disappeared. The 

 cell-substance has collected at one end of the nucleus as an 

 elliptical granular mass, and appears separated from it by a 

 transparent, clear bag." 



" In the next stage the nucleus becomes flattened and dis- 

 coid, so that when viewed from the surface it is broad and cir- 

 cular, but appears narrow and staff-shaped when seen in profile. 

 The cell-substance at this time is drawn out into a cylindrical 

 or club-shaped granular body, separated from the nucleus by 

 a shorter or longer clear tube, the former clear bag. At the 

 front part of the nucleus is seen a short and tapering curved 

 projection, and at its hind end viz., that directed toward the 

 clear tube and cell-substance there is also to be found a short- 

 pointed process extending into the clear tube just named." 



" In the next stage the nucleus becomes more flattened and 



