SPERMATOGENESIS OF THE HORSE. 299 



to distinguish from other nuclear bodies when such are present 

 (Figs. 8-1 1). The small spherical nucleolus again appears to 

 be fairly constant, though at times it is difficult to distinguish it 

 from the other bodies. 



2. Synizesis and Growth Period. 



After a brief period of rest the cells begin to increase in size. 

 For some time the nucleus appears much the same as it does in 

 the resting stage of the spermatogonia (Fig. 8). Later it becomes 

 more granular and the linin fibers become more distinct (Fig. 9). 

 Soon after, the chromatin threads become massed in the center 

 of the nucleus (Fig. 10), and later the nuclear wall expands and 

 the entire mass passes to one side of the nucleus, leaving a large 

 clear area in the remaining portion (Fig. li). This condition 

 is much the same as in the pig except that in that animal the 

 nucleoli were invariably found within the mass of threads and in 

 a position nearest to the nuclear wall, while in the horse the 

 nucleoli are almost invariably within, or next to the clear area 

 (Fig. n). The nuclear wall in this stage is often very irregular, 

 especially next to the clear portion of the nucleus. 



Shortly after the collapse of the chromatin material, the threads 

 pair and appear in about half the original number and twice 

 as thick (Figs. 10-12). There is considerable evidence that 

 pairing of the threads takes place by parasynapsis, and nothing 

 was observed which would indicate that it takes place otherwise; 

 but this phase of the problem demands more study and no 

 positive statement can be made in regard to it at this time. 

 The entire mass of threads then moves toward the center and the 

 large clear area disappears (Fig. 12). The large nucleolus passes 

 toward the periphery of the nuclear wall and the threads soon 

 become evenly distributed. Then follows the period of growth 

 during which time both the nucleus and c} r toplasm increase 

 greatly in size (Figs. 13 and 14). The chromatin threads and 

 the large nucleolus also increase considerably in size. It is 

 between the synaptic stage and the fully developed spireme 

 stage that the chromatoid body makes its appearance (Figs. 

 12-14). 



