THE BIOLOGY OF THE CELL SURFACE 



round or oval flask with a long neck. In earlier stages this 

 neck appears solid; in later stages it is really a tube, as 

 Figs. 2()d and 2()e show. 



Now in this stage the structure of the middle-piece gran- 

 ule and its relationship to the sperm-nucleus are most 

 clearly discerned. The sperm-nucleus and the middle-piece 

 granule form one continuous complex. The tip of the tube 

 arising from the base of the sperm-head spreads out slightly 

 as very delicate threads to connect with the minute granule 

 which arose from the middle-piece body. Thus, the middle- 

 piece granule resembles the top of a parachute, the threads 

 of which come together at the tip of the sperm-tube. At 

 this junction another granule is often found. 



With the apposition of the nuclei, the sperm-nucleus 

 loses connection with the middle-piece granule. This is 

 shown in Figs. 29/ and g. There is never a re-establish- 

 ment; in the succeeding stages in mitosis leading to first 

 cleavage, the granule may lie as a discrete single inert body 

 at any point in the cytoplasm with reference to the spindle. 

 I have never found any evidence of its division or of its 

 taking up a position at either spindle pole. By the time 

 that the nuclei come into apposition, the more minute 

 granules can no longer be traced. 



Within the egg the sperm-head, a structure notable for 

 its low water-content, at first maintains its shape and size 

 but as it is carried from the periphery of the egg it slowly 

 approaches spherical form, increasing in volume and its 

 outline losing definition. Observations on eggs fixed during 

 this period reveal what the living egg does not so clearly 

 show: namely, that the transformation of the sperm-head 

 into a vesicular nucleus is the resolution of a greatly con- 

 densed mass of chromatin — an exaggerated and rapid evolu- 

 tion of chromosomes from telophase condition to that of a 

 resting nucleus. Though this process is more easily visible 

 before the sperm-nucleus unites with that of the &g%, never- 



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