566 Theophilus s. Painter, 



d) During- this period the leptotene-threads lie scattered through 

 the nuclear cavity. 



e) Synizesis. 



f) The autosomes emerge from the contraction as thick segmented 

 threads which have a ''bouquet form". This is the pachytene stage. 



g) Diplotene stage, when the longitudinal split appears in the 

 pachytene-threads. 



h) Second contraction during which the autosomes take on the 

 form which they will have during the first division. This stage 

 has three phases, in spiders. First a twisting of the diplotene- 

 threads takes place. Second, there is an untwisting phase. Third, 

 the shape of the autosome in assumed. 



i) Very early prophase stage when the chromosomes lie scattered 

 through the nuclear cavity, but before the nuclear wall dissolves. 



j) First divison of autosomes. 



k) Distinct resting stage for the young second spermatocytes. 



1) Second spermatocyte division, 

 m) Formation of mature spermaform spermatids. 



These stages show with more or less clearness in all of the 

 spiders studied so far. No "confused stage" has been seen in any 

 of my preparations. 



The question of reduction. 



As Wilson (VIII) has pointed out, we shall not be able to 

 solve this problem until we determine what goes on during synizesis. 

 No spider has been found which was instructive at this period. 

 After the synaptic contraction, however, it has been possible to 

 follow the course of the autosomes in a detailed way. It seems 

 wortli while, to discuss this later behavior as it throws some light 

 on what has taken place earlier in the growth period. Perhaps at 

 some later time it will be possible to fill out the missing chapters in 

 tlie history of the germ cells. 



Before synapsis, we have the thin leptotene-threads lying 

 scattered through the nuclear cavity with no api)arent arrangement. 

 'J'iien they are drawn to one side of the nucleus. After the con- 

 traction we have very heavy threads which sooner or later show a 

 split. These threads are much less numeious than the leptotene- 

 threads of the presynaptic period. If these facts, together with the 

 appearance of bivalent chromosomes in the first division, constitute 

 sufficient proof for a pairing of homologous leptotene-threads, then 



