IOO 



THE GERM-CEU.S 



entiated into a fin-like undulating membrane. The axial filament 

 may be traced through the middle-piece up to the head, at the base of 

 which it terminates in a minute body, single or double, known as 

 the end-knob, and not improbably representing the centrosome. 



There is still some doubt regarding the nature and functions of 

 these various parts. The nucleus is proved both by its origin and 

 by its history during fertilization to be exactly equivalent to the 

 nucleus of the mature egg. The middle-piece and the tail represent 



Fig. 48. Spermatozoa of fishes and amphibia. [BALLOWITZ.] 



A. Sturgeon. B. Pike. C. D. Leuciscus, E. Triton (anterior part). F. Triton (posterior 

 part of flagellum). G. Raja (anterior part), a. apical body ; ^.end-piece; f. flagellum ; /. end- 

 knob (? centrosome) ; m. middle-piece; n. nucleus; s. apical spur. 



the principal mass of the cytoplasm of the sperm-cell, and the mid- 

 dle-piece is probably to be regarded as merely the thickened basal 

 portion of the flagellum. 



The principal uncertainty relates to the position of the centro- 

 some. It is certain that in most cases the centrosome or attraction- 

 sphere lies in the middle-piece ; for from it the centrosome arises 

 during the fertilization of the e^, in every ac-ci'iate'y known ease. 

 In a few cases, moreover, i-lie middle-piece has been traced back to 



