140 J. DUESBERG 



three or more (fig. 3 on the left below) . So unvarying are these 

 features that I feel justified in considering these cells as a distinct 

 generation of spermatogonia and term them 'secondary sperma- 

 togonia.' The primary and secondary spermatogonia are in 

 close contact with each other, the cystic cavity being at these 

 stages only virtual, in contrast with all later stages, when some 

 room, in well fixed material, is left between the cells. 



The spermatogonia belonging to a third generation are, if any, 

 not much smaller than the secondary spermatogonia. In the 

 nucleus several blocks of chromatin are present. The chondrio- 

 somes are granules, most of them regular, some larger and 

 coarser. Instead of surrounding the nucleus, as in the preceding 

 generations, they are all located at one of its poles (fig. 6). 

 During mitosis a breaking-up into smaller granules appears to 

 take place. Their behavior is the same as described above and 

 is illustrated for the stage of metaphase by figure 7. In fact, 

 the size of the spindle is in proportion to the size of the cell so 

 large that the chondriosomes have to take whatever place they 

 can in the cell-body, which is practically filled by the karyo- 

 kinetic figure. 



In the first spermatocytes (fig. 8) the polar location of the 

 chondriosomes persists throughout the whole growth-period until 

 the prophase of the first division and coincides as always with the 

 polar field, while in the nucleus the usual structural changes take 

 place. The chondriosomes are now granules all equal in size 

 and regularly spherical and most of them are very closel}^ heaped 

 together. It must be noted that during this so-called growth- 

 period the spermatocytes of Fundulus actually grow very little 

 and that there is no evidence, as in other spermatocytes, of an 

 increase in the mass of chondriosomes. 



At the prophase of the first division the mitochondria become 

 scattered all around the nucleus and, when the spindle is formed, 

 they are as previously pushed towards the periphery of the cell- 

 body and very close to it ; for here again the spindle is very large 

 in proportion to the cell. I may mention in passing that the 

 centrioles appear very conspicuously at the poles of the spindle 

 (fig. 9). During the anaphase all the mitochondria are found 



