150 ON THE SPERMATOGENESIS OF THE SILK-WORM. 



2. The primary sperm-cell resembles very much the primary 

 egg-cell, and is conical in shape and contains a nucleus in its 

 broad end. Its nucleolus always consists of an aggregation of 

 chromatin granules, whose number varies from two to four or 

 more. It divides many times in the usual karyokinetic manner, 

 and the cell-body gradually decreases in size until it becomes 

 about two-thirds or less of the original cell. It is then called 

 the sperm-mother-cell and passes to the growing stage. 



3. In the early part of the growing stage, the sperm-mother- 

 cell has an ordinary resting nucleus with the chromatin granules 

 scattered in it. It gradually becomes larger, and with this 

 the change of nucleus takes place. The chromatin granules 

 first gather themselves to one side of the nucleus and form an 

 irregular mass from which fine achromatic fibres radiate. This 

 chromatin mass, dissolves and a fine skein stage with a nucleolus 

 is formed. The chromatin granules of this skein again dissolve 

 into many isolated granules and the nucleus again assumes a 

 granular structure. There are now two nucleoli in each nucleus. 

 These nucleoli pass out into the cytoplasm one after the other. 

 An achromatic spindle is also seen at this stage, formed from 

 cytomicrosomes. This spindle consists of two parts, the central 

 and the polar, which latter seems to be derived from the nucleus 

 together with the centrosomes. The granular chromosomes, 

 now again collect themselves and form \ ring-like structures. 

 Each of these rings dissolves again into four chromosomes and 

 forms " Kernplatte." 



4. The sperm-mother-cells contain at first twenty-eight 

 chromosomes. In the first division each of these divides trans- 

 versely to its long axis and forms two chromosomes, of which 

 one goes to one pole and the other to the opposite pole. The 

 daughter-cells thus contain each twenty-eight chromosomes as 

 the mother-cell. 



The nuclei of these daughter-cells form no resting stage, 

 and directly pass over to the second division in which half the 

 number of chromosomes goes to one cell and the other half to 

 the other. The grand-daughter-cells thus formed contain there- 

 fore only fourteen chromosomes, which is half the number of 

 the mother-cell. 



5. After this division, the fourteen chromosomes collect at 



