ORIGIN OF HEAD AND TAIL OF SPERM 



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becomes differentiated into a sperm in the following way. 

 A delicate filament of protoplasm (B, /) grows out on one 

 side, and at the same time the nucleus (nit) retreats to the 

 opposite extremity (c F). Next the protoplasm draws itself 

 away, as it were, from the nucleus and forms a kind of swel- 

 ling (G and H, x) round the base of the filament, which in- 

 creases considerably in length. The filament is now recog- 



FIG. 60. Spermatogenesis in the Rat. 



A, Sperm-cell : nu, the nucleus. 



B, first indication of the tail (/) as a protoplasmic filament. 



C-F, further growth of the tail, and retreat of the nucleus (mt) to 

 the opposite end of the cell to form the head. 



G, H, separation of protoplasmic globule (it), afterwards cast off. 

 I, fully formed sperm. (After H. H. Brown.) 



nizable as the flagellum or tail of the sperm, the nucleus 

 as its head. The lump of protoplasm (x} at the junction 

 of head and tail assumes the form of a globule attached 

 only by one side (H) : this gradually separates itself from 

 the now fully-developed sperm, and is finally completely 

 detached (i). 



Thus a sperm is a true cell, the nucleus being represented 

 by the head, and the cell-body by the tail. But it is to be 



