SPERMATOGENESIS OF LEPISMA DOMESTICA 403 



Synapsis and reduction 



It has not been possible in the ordinary chromosomes or auto- 

 chromosomes to see whether there is either a side-by-side union 

 of the spireme threads, a parasynapsis, or an end-to-end "conju- 

 gation, a telosynapsis. It is clear, however, that the spireme 

 threads in postsynaptic stages are much thicker and are present 

 in fewer numbers. Whether they are half the leptotene number 

 or not could not be made out. 



In the case of the idiochromosomes the conclusions are clearer. 

 Each idiochromosome breaks up into a spireme thread and the 

 two threads eventually unite end to end, one of them being 

 attached to a large plasmosome. From these threads two 

 chromosomes are formed by the condensation of the chromatin, 

 but they still remain united by a thread which is probably 

 linin in nature and along which, when the thread lengthens, 

 the chromatin is drawn out. 



Synapsis, or a side-by-side conjugation, if it takes place at 

 all, does so following the telophase of the first maturation division. 

 That the idiochromosomes do come into a very close relation is 

 shown by the longitudinal split apparent in the idichromosome 

 nucleolus of the resting nuclei of the second spermatocyte (figs. 

 47 and 50). 



If, as is generally conceded, the spermatogonial chromosomes 

 represent two groups, one of maternal and the other of paternal 

 chromosomes, and the homologous pairs conjugate at synapsis 

 then each of the idiochromosomes represents one spermatogonial 

 chromosome. A further proof of this is that the thirty-four 

 spermatogonial chromosomes, judged from their size, are all of 

 the same valence, i.e., bivalent. After synapsis the autochro- 

 mosomes are quadrivalent, but definite four-part tetrads are not 

 apparent during the prophase, and at the metaphase the chromo- 

 somes are dumb-bell-shaped, the longitudinal pairing leaving 

 no trace. However, in one cell I have found the idiochromosomes 

 at the time of anaphase showing a bivalent construction (fig. 

 45). 



