I50 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 
