SPERMATOGENESIS 



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(F, G), while the nucleus constitutes its more or less spindle- 

 shaped head, and the centrosome is included in a small 

 middle piece at the junction of head and tail. 



Thus the sperm or male gamete is a true cell, specially 



FIG. 149. Spermatogenesis in the Mole-Cricket (Gryllotalpa). 



A, primitive sex-cell, just preparatory to division, showing twelve chromosomes 

 (chr) ; c. the centrosome. B, sperm-mother-cell, formed by the division of A, 

 and containing twenty-four chromosomes ; the centrosome has divided into two. 

 C, the sperm-mother-cell has divided into two, each daughter-cell containing 

 twelve chromosomes. D, each daughter-cell has divided again by a reducing 

 division, a group of four sperm-cells being produced, each with six chromosomes. 

 E, a single sperm-cell about to elongate to form a sperm. F, immature sperm ; 

 the six chromosomes are still visible in the head. G 5 fully formed sperm. 

 (From Parker's Biology ', after vom Rath.) 



modified in most cases for active movement. This actively 

 motile, tailed form is, however, by no means essential : in 



