242 Thomas H. Montgomery, Jr., 



the largest of tlie yolk particles, and is already indicated in the 

 follicular egg, but it is more sharply marked at oviposition and the 

 columns become longer, that is more of the yolk enters into their 

 formation with the advance of age.^) The boundary between the 

 two yolk layers is quite a definite one (Fig. 4), and Gilson's fixa- 

 tive frequently causes a dislocation of the two at this point. The 

 inner yolk is composed of irregularly polygonal particles which are 

 smallest at the centre of the egg. 



The cytoplasm forms a thin envelope around the whole yolk 

 mass and is present in larger quantities around the polar spindles 

 and the sperm nuclei, but its total amount is very small compared 

 with the mass of the yolk substance. Its peripheral layer is not 

 divided into cell territories as Balbiani had described. The growth 

 of the ovarian egg shows that the cytoplasm becomes graduall}^ 

 filled with yolk, while it does not increase perceptibly in amount, 

 and the latest ovarial ova show all the yolk particles imbedded 

 in cytoplasm. But in the egg at oviposition most of the cytoplasm 

 is at the surface, around the sperm nucleus and the polar spindle, 

 while in the remainder of the egg almost no cytoplasm is to be 

 seen except on very favorable fixation when a delicate meshwork 

 of it appears. 



At oviposition the egg is already fertilized with the sperm 

 nucleus about half way between the periphery and the centre, and 

 contains the first polar spindle (Fig. 6). The sperm nucleus (Fig. 8) 

 is slightly elongate, and dense save for a few small vacuoles; it 

 lies in a large accumulation of reticular cytoplasm containing minute 

 yolk spherules, and beyond these the larger yolk masses. There is 

 no indication of either centrosome or aster in connection with it. 

 The first polar spindle is in the late anaphase (Fig. 7), shows no 

 trace of centrosomes, and is composed of two plates of small chromo- 

 somes joined by distinct connective fibres; it is at the surface of 

 the egg in a thickening of the superficial cytoplasm. The chromo- 

 somes are dyads, and have become much smaller and denser than 

 in the preceding prophase (Figs. 2a, 2b). I had only a few sections 

 showing such spindles, could not find them on surface views, and 

 accordingly was unable to determine the number of chromosomes at 



1) From the 4cell stage of cleavage on the centre of the egg is 

 fluid, and into this central fluid cavity extend the inner ends of the yolk 

 columns. This fluid may be a disintegration of a part of the yolk. 



