1910.] NATURAL SCIENCES OF PHILADELPHIA. 303 



In the next .stage, or late post-synapsis (figs. 20 and 21), the threads 

 are somewhat contracted but more widely spread throughout the 

 nucleus. In smear preparations (figs. 19, 20 and 21) the spireme of both 

 early and late post-synapsis shows a longitudinal split which corresponds 

 To a similar split in the last spermatogonial spireme (as seen in cyntliia). 

 The spireme now segments into the reduced number of chromosomes 

 (fig 22) : in smear preparations it may still show the longitudinal split 

 of the late synapsis stage; in sections, where there is always a greater 

 concentration of chromatin granules, the spireme is shown segmented 

 into loops which have their middle point marked either by a thinner 

 part or by a slight knob-like projection. This marks the plane of the 

 first division (fig. 22). During the growth stage the spermatocyte 

 greatly increases in size, while its basi-chromatin almost completely 

 loses its staining property and becomes loose and indefinite in structure. 

 This is true only in part, for in smear preparations, in which the chro- 

 matin segments stain less deeply but never entirely lose their identit} 7 

 (fig. 26), the chromosomes are seen as faintly staining bodies made up 

 of chromomeres joined by linin threads. It is at this period that, for 

 the first time, a spheroidal, darkly staining body appears and stands 

 out in sharp contrast to the faintly stained nucleus ; it is usually eccen- 

 trically placed, and is often seen dividing so that it may appear as two 

 separate bodies or as a dumbbell (fig. 23). Its appearance, behavior, 

 and staining reaction suggest its similarity to the accessory chromosome 

 of McClung, the chromatin nucleus of Montgomery (1901), the hetero- 

 tropic chromosome or idiochromosome of Wilson, and the odd chromo- 

 some of Stevens; while its frequent dyad nature during the growth 

 period, indicating its bivalence, and its subsequent behavior, relate 

 it to the third type described by Wilson, in which the idiochromosomes 

 are of equal size. Following the terminology of Wilson, I shall call this 

 body the idiochromosome. 



3. Prophase of First Maturation Division. — In preparation for the 

 first maturation division the chromatin again assumes its staining 

 property and definite groups of chromatin granules appear upon the 

 spireme, the nineteen aggregations of basi-chromatin which have been 

 distinguishable throughout the growth stage in smear preparations 

 now become more clearly defined, the longitudinal split of the spireme 

 is still seen and each chromosome is joined to the other by a continuous 

 linin thread (fig. 26). A similar condition is seen in sections where each 

 chromosome shows a longitudinal split, while some of the chromosomes 

 are beginning to join to form rings (fig. 27). In a little later stage the 

 segments have opened into ring-like granules (figs. 32 and 28) and 

 20 



