GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 1 25 



■ ' ' f '% i^' »iJ 



Fol was in error in referring it to the tip. Field's conclusion is there- 

 fore almost certainly erroneous, and he has probably confounded the 

 centrosome with the " Nebenkern " or paranucleus. 



Diametrically opposed, moreover, to the results of Platner and 

 Field are those of Hermann ('89) and Calkins ('95, 2) on amphibia 

 and earthworms, and 

 both these observers 

 have devoted especial 

 attention to the origin 

 of the middle-piece. 

 The evidence brought 

 forward bv the last- 

 named author, whose 

 preparations I have 

 critically examined, 

 seems perfectly con- 

 clusive that the at- 

 traction-sphere or 

 centrosome passes 

 into the middle-piece. 

 The " Nebenkern," 

 which is rarely pres- 

 ent, appears in this 

 case to take no part 

 in the formation of 

 the fiagellum, but 

 degenerates without 

 further change. In 

 the salamander the 

 origin of the middle- 

 piece has been care- 

 fully studied by 

 Flemming and Her- 

 mann. The latter 

 ('89) has traced the 

 middle-piece back to 



Fig. 63. — Formation of the spermatozoon from the sper- 

 matid in the salam.mder. [HERMANN.] 



A. Young spermatid showing the nucleus above, and below 

 the colorless sphere, the ring, and tlie chromatic sphere. 

 B. Later stage, showing the chromatic sphere and ring at the 

 base of the nucleus. C. D, E, F. Later stages, showing the 

 transformation of the chromatic sphere into the middle-piece m, 



an " accessory body " 



(Nebenkorper), which he believes to be not a " Nebenkern " 

 (derived from the spindle-fibres), but an attraction-sphere derived 

 from the aster of the preceding division, as in Liunbricus. This 

 body differs greatly from an ordinary attraction-sphere, consisting 

 of the following three parts lying side by side in the cytoplasm 

 (Fig. 63). These are: {a) a colourless sphere, {b) a minute rounded 

 body which stains red with saffranin like the nucleoli or plasmo- 



