CHAP, i.] MALE ORGANS. 367 



i 



nucleus known as karyomitosis or karyokinesis, and gives rise 

 to two cells, one of which remains to fill the place of the mother- 

 cell in the outer layer, while the other advances inwards towards 

 the centre of the lumen. The latter undergoes repeated karyomi- 

 tosis, and so gives rise to a number of cells characterized by the cell- 

 substance being small in bulk relatively to the nucleus. Whether 

 each division of the nucleus is from the first accompanied by a com- 

 plete division of the cell-body, or whether a number of nuclei are 

 formed in a coherent mass of cell-substance, which is subsequently 

 partitioned out among the nuclei, is a question which we may leave 

 on one side ; the important thing is that a mother-cell by mitosis 

 gives rise to a brood of small daughter-cells. Each daughter-cell 

 soon assumes an oval or club-shaped appearance, with the nucleus 

 at one end. Changes then take place in the nucleus ; into these we 

 cannot enter, but may say that they appear to consist in the ejec- 

 tion or separation of a part of the nucleus, and a transformation 

 of the rest, so that what was an ordinary nucleus becomes the 

 differentiated head of a spermatozoon. At the same time the- 

 cell-body is transformed into the middle piece from which the 

 tapering tail subsequently grows out. 



In a transverse section of a tubule it is easy to recognize that 

 while some of the nuclei in the outer layer of cells are undergoing 

 this mitosis, others are completely at rest ; the latter are regarded by 

 many not as simply nuclei undergoing a temporary rest before they 

 once more undergo mitosis, but as nuclei belonging to other kinds 

 of cells which do not themselves give rise by division to sperma- 

 tozoa but which possessing a branched cell-substance, are arranged 

 at intervals along the circumference of the tubule so as to 

 radiate inwards, like the spokes of a wheel, towards the centre 

 of the lumen, thus furnishing a framework in the spaces of 

 which the active, dividing, spermatozoa-forming cells are lodged. 

 And it is maintained that these cells perform an important 

 subsidiary function, by assisting in some way or other in the 

 development of the spermatozoa ; it is urged that the cells about to 

 become spermatozoa are for a while lodged in the cell substance of 

 these branching cells, and there undergo their full development, and 

 that the grouping of the spermatozoa into radiating bundles is 

 due to their aggregation in connection with these radiating cells, 

 and not as might otherwise be supposed to each bundle having a 

 common origin from a single mother cell. In any case the sper- 

 matozoa from one of the mother cells of the outer layer seem 

 to be supported and held together by a fine reticulum, either 

 belonging to the cells just spoken of or supplied by the cell bodies 

 of cells which like the spermatozoa arise from the division of 

 mother cells, but which do not become developed into sperma- 

 tozoa. For there seems reason to believe that besides the cell- 

 division which gives rise to the spermatozoa, other cell-divisions 

 are taking place ; and the products of these may fulfil the above 



