188 S. W. GEISER. 



insect testes, it is possible to find all stages of the process, each 

 in a different phase, in a single section. 



(b) Later Stages in Maturation. Lcptotene. Synapsis. 

 Pachytene. In the further maturation of the male germ-cells 

 of Gambusia the process follows the usual path. There are no 

 features worthy of special note. The filamentous chromosomes 

 of the leptotene (Figs. 11-16) are produced by a condensation 

 of the chromatin on the linin fibrils. There has not been any 

 striking evidence of pairing of the chromosomes in the leptotene, 

 owing largely to the difficulty of the material. In the synaptene 

 and pachytene stages (Figs. 17-18) which follow upon the lepto- 

 tene there is evidence that parasynapsis occurs. The chromatin 

 threads in early synapsis become only half as numerous as in 

 the leptotene. The pachytene shows the typical orientation of 

 the thickened and shortened threads of this stage. No contrac- 

 tion-stages (synisesis) appear to occur in this species. 



(c) Tetrads and Diakincsis. The tetrads in their early stages 

 appear to be of the open-ring type (Figs. 20-21). They contract 

 however, as they take on the peripheral position characteristic 

 of diakinesis (Fig. 22) until all trace of their tetrad character 

 is lost. They then appear as large, spherical, deeply-stained 

 bodies evenly distributed through the plasm just beneath the 

 nuclear surface. In this position they remain for some little 

 time, after which they gather to form an equatorial plate (Fig. 



23)- 



The tetrads are halved in the I.-Spermatocyte metaphase. 

 The distribution of the dyads to the two daughter cells of the 

 first spermatocyte division could not be made out (Figs. 24-26). 

 The II. -Spermatocyte division follows immediately upon the 

 conclusion of the first division, with no nuclear reconstitution. 

 After the secondary spermatocyte division is completed the 

 chromosomes clump together, the chromatin changes in reaction 

 to stains and becomes scattered throughout the nucleus. After 

 the resultant spermatid nucleus has been constituted, a rather 

 long interkinesis occurs. This is followed by a stage in which 

 the chromatin gathers at the periphery of the nucleus and stains 

 deeply. 



