214 Sargant. — Formation of the Sexual N tic lei 
they increase in size during this period, and are much com- 
pressed in the narrow pollen-tube l . 
In describing the three later nuclear divisions of the 
spermatogenetic series, I have said nothing as to the number 
of chromosomes which take part in them. There were 
difficulties in the way of exact counting, but about twelve 
chromosomes are found on each spindle. 
Homotype and Heterotype Divisions. 
The four nuclear divisions included in the spermatogenetic 
series of L ilium Martagon have now been described in detail. 
One characteristic — and that the most important — they 
possess in common with each other, with the three oogenetic 
divisions, and with the ordinary vegetative division. In each 
of these cases the effect of the whole process of karyokinesis 
is to divide each parent chromosome into a pair of daughter- 
chromosomes by longitudinal fission, and to build up duplicate 
daughter-nuclei from the duplicate sets of daughter-chromo- 
somes thus formed. 
Less uniformity is observed when we come to detail. The 
seven nuclear divisions of the spermatogenetic and oogenetic 
series are distinguished from all others by the possession of 
twelve chromosomes in place of twenty-four. Among these 
seven divisions thus naturally divided from the rest, two 
distinct types of karyokinesis are found. One differs from 
that of the vegetative nucleus only in the number of chromo- 
somes. The other differs widely from the vegetative type in 
many respects besides that of number, and is characteristic 
of the first division in either series — that division in which the 
reduced number of chromosomes first appears. 
I have already insisted sufficiently on the peculiar character 
of the first karyokinesis on either side. The fact that the 
nuclear divisions, occurring at so critical a period in the line 
of descent of both sexual nuclei, should not only differ from 
the usual type, but also resemble each other so closely, is 
Guignard, 1. c., p. 178 and Fig. 36. 
