STUDY OF CHROMOSOMES OF LACHNOSTERNA. 87 



gonial area of the testes are in this stage and apparently it is of 

 of much longer duration than the reticular or "resting" stage. 



In some respects the chromatic blocks above described cor- 

 respond to the " prochromosomes " which -have been described 

 by Overton ('09) in Podophyllum, Arnold ('08) in Hydrophilus 

 piceus, Goodrich ('16) in Ascaris incurva and other workers. 

 In these cases, however, the chromatic bodies appeared at the 

 beginning of the growth period and, according to the above 

 workers, these bodies arranged themselves in pairs, thereby 

 accomplishing the synaptic process. In Lachno sterna there is no 

 such paired arrangement of the chromatic blocks; they merely 

 represent stages in the formation of the spermatogonial chro- 

 mosome groups and might really be called prophases, except 

 that they are of relatively long duration. In some cases a 

 precocious longitudinal split can be detected, preparing the 

 chromosome for the next cell division. 



2. The Synaptic Stages and Maturation Divisions. 



Following the telophase of the last spermatogonial division 

 (Fig. 13), the chromosomes spin out in the form of very fine 

 (leptotene] threads (Fig. 18, 19) which entirely fill the nucleus and 

 prevent a minute analysis of this stage. The actual pairing of 

 the homologous chromosomes could not be followed in detail, 

 but observations on a few favorable cells (Fig. 19) indicate that 

 the union is side-to-side (parasynapsis) . Stevens ('06) has 

 described telosynapsis in the Coleoptera, but she did not make a 

 study of the early growth stages. 



The leptotene stage gradually merges into a definite contrac- 

 tion stage (synezesis) with all the chromatic threads polarized 

 at one side of the nucleus (Figs. 20, 44). These stages are 

 always found in a definite part of the testes, namely in region B 

 (Fig. 2), and are found nowhere else. McClung ('05) used the 

 word "synezesis" to describe that "condition of the nucleus in 

 which the chromatin is found massed at one side of the vesicle, 

 without regard to whether it is a normal phenomenon or not." 

 McClung and recently some of his students, Whiting ('17) and 

 Hance ('17), have maintained that a unilateral massing of the 

 chromatin or synezesis is an artifact and is due to improper 



