254 



SPERMATOGENESIS AND OOGENESIS less. 



distinguished by a peculiar condition of tlie nucleus. We 

 saw (p. 65) that the number of chromosomes is constant in 



Fig. 60.— Spermatogenesis in the Mole-Cricket [Gryllotalpa). 



A. Primitive sex-cell, just preparatory to division, showing twelve 

 chromosomes (ckr) ; c, the centrosome. , . 



B. Sperm-mother-cell, formed by the division of A, and contaming 

 twenty-four chromosomes. The centrosome has divided into two. 



c. The sperm-mother-cell has divided into two by a reducing division, 

 each daughter-cell containing twelve chromosomes. 



D. Each daughter-cell has divided again in the same manner, 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. Fully formed sperm. 

 (After von Rath.) 



