124 



GENERAL EMBRYOLOGY 



the need for an easily available food supply ^for the large 

 number of sperm cells during their metamorphosis. 



Probably the most interesting phase of the cytoplasmic as- 

 pects of spermatogenesis is this metamorphosis of the sper- 



FIG. 70. Formation of the spermatozoon in Urodeles. From 

 "Cell," A-E, Salamandra, after Meves; F-K, Amphiuma, after McGregor. 

 A. Spermatid with peripheral pair of centrosomes (c) lying outside the sphere, 

 and axial filament. B. Centrosomes near the nucleus, outer one ring-shaped; 

 a, acrosome. C. Inner centrosome inside the nucleus, enlarging to form middle 

 piece; n, nucleus. D. Portion of much older spermatid, showing divergence of 

 two halves of the ring, r. E. Portion of mature spermatozoon, showing upper 

 half of ring at r, and the axial filament proceeding from it. F. Spermatid of 

 Amphiuma, showing sphere-bridges and ring-shaped mid-bodies. G. Later 

 stage; outer centrosome ring-shaped, inner one double; sphere, s, converted into 

 the acrosome, a. H. Migration of the centrosomes. /. Middle-piece at base 

 of nucleus. J. Inner centrosome forms the end-knob within the middle-piece, 

 which is now inside the nucleus. K. Enlargement of middle-piece, m, end-knob 

 within it; elongation of the ring. 



matids into spermatozoa. After growth and maturation the 

 sjDgrmatids have much the same external appearance as any 

 typical cell; they are more or less spherical cells with a pair of 



