CENTRIFUGING THE SPERMATOCYTE CELLS 339 



been found by Lyon ('07), Morgan ('10) and Lillie ('08) that 

 there are at least three layers of materials segregated out by the 

 centrifuge. There is at the centripetal pole a gray cap, then a 

 layer of clear protoplasm, and at the distal pole a mass of yolk 

 and pigment. This is true in the eggs of Arbacia, Asterias, 

 Nereis, Chaetopterus, Phascolosoma, Cerebratulus and Cumingia. 

 The gray cap, in some cases at least (Nereis, Chaetopterus, 

 Cumingia) is formed of oil drops and corresponds therefore, in 

 nature and in position to the cap of oil drops in the centrifuged 

 spermatocyte cells. The middle layer of clear protoplasm is 

 practically the same in the two cases. The heaviest material in 

 the egg cells is the yolk and pigment, and this therefore corre- 

 sponds with the mitochondria in the spermatocyte cells, but 

 whether any of the mitochondria have the same function as the 

 yolk spheres of the marine egg is questionable. In a very recent 

 paper, Beckwith ('14) has shown that there are also three layers 

 in the centrifuged eggs of Hydractinia, and she has been able to 

 distinguish between yolk and mitochondria, which are mingled 

 together at the distal pole. This is the first attempt, so far as 

 I know, to segregate the mitochondria from the protoplasm by 

 experimental methods, and it is interesting to find that her 

 results for the egg tally with my own for the spermatocyte cells. 

 In comparing the unfertilised marine egg and the resting sper- 

 matocyte cell of Notonecta the resemblance is very striking. The 

 normal cells in the two cases show a close similarity in appearance, 

 and react in the same way to the centrifuge. In the case of the 

 egg, the germinal vesicle is forced toward the centripetal pole by 

 the centrifuge, and the nucleolus to the distal end of the nucleus. 

 The nucleus and the karyosphere in the spermatocyte cells take 

 the same relative positions. In the dividing cells of the marine 

 eggs, it has been found in general that the mitotic figure remains 

 intact when the cells are centrifuged, just as it does in the divid- 

 ing spermatocyte cells. The whole figure may be shifted in the 

 eggs so as to lie in the clear protoplasm. This does not occur 

 to any considerable extent in the spermatocyte cells, though there 

 might be a very slight shifting in some cases. 



