1908] GATES— REDUCTION IN OENOTHERA 15 



nothing in the manner of segmentation of the spirem to indicate this. 

 However, it is clear enough that one chromosome frequently swings 

 around, as already mentioned, and pairs with its neighbor on the 

 spirem. We do not really have, then, a transverse division of chromo- 

 some bivalents, but a separation of whole (somatic) chromosomes. 

 Nothing has been found in the earlier stages which would correspond 

 to the gamosomes and zygosomes of Strasburger, and even should a 

 pairing of parallel threads during synapsis occur (a possibility which 

 will be discussed later), the final pairing is between chromosome 

 bodies which were lying end to end on a single spirem thread. 



The linin connections during diakinesis appear to be merely the 

 more finely drawn out portion of the spirem between the chromosomes. 

 As condensation and contraction of the chromosomes progress, 

 these linin connections become longer and more delicate (figs. 31, 33). 

 The chromosomes become more dense and compact, being at first 

 oblong-cylindrical (figs. 24, 26) and then more nearly globular or 

 pear-shaped (fig. 31). Certain chromosomes sometimes undergo this 

 contraction more quickly than others, as in fig. 2Q, and the different 

 stages of this condensation may occasionally all be found in the same 

 nucleus. In other cases the globular appearance is due to the 

 position in which certain chromosomes happen to be lying (fig. 34). 



HETEROTYPIC MITOSIS 



During the prophase stages last outlined the cytoplasm usually pos- 

 sesses a more or less obscurely radiate appearance. A felt-work 

 of fibrillae finally appears around the nuclear membrane. Later 

 these fibrillae come to run tangentially to the latter, terminating in the 

 cytoplasm, and by their aggregation in certain regions the multipolar 

 spind'e is formed. From this stage the fibers are rearranged to form 

 the bipolar spindle, passing through conditions in which the spindle 

 appears quadripolar or tripolar in section. In the meantime the 

 nuclear membrane has dissolved and the chromosomes are found 

 at first in a cavity surrounded by fibers which preserve the outline of 

 the nuclear wall. Later they come in and become attached to the 

 chromosomes. Usually the large nucleolus has vanished before this 

 time, but occasionally it may still be seen (fig. 35). In fig. 37 the 

 small nucleolus is shown, which can very frequently be seen at this 



