98 



GENERAL EMBRYOLOGY 



n 

 ac 

 pc 



= s 



mi 



a 



af 



FIG. 51. Flagellate sper- 

 matozoon. A, B. Two views 

 of human sperm cell. After 

 Retzius. X 2000. C. Dia- 

 gram of the structure of a 

 generalized type of flagellate 

 spermatozoon. After 

 Meves. a, annulus; ac, 

 anterior centrosome; af, ax- 

 ial filament; c, centrosomes 

 (end knobs) ; e, protoplasmic 

 envelope; h, head; m, middle 

 piece; mi, mitochondria; n, 

 nucleus ; ne, neck ; p, perf ora- 

 torium (acrosome) ; pc, pos- 

 terior centrosome; s, spiral 

 filament; /, tail piece; if, 

 terminal filament. 



enlarged forming the so-called head. 

 This is in reality chiefly made up of the 

 nucleus of the cell, and it stains densely 

 with all nuclear dyes. The chromatin 

 of the nucleus is solidly packed, and 

 though the head of the sperm is much 

 smaller than the egg nucleus, the two 

 contain practically, perhaps precisely, 

 equal amounts of chromatin. Just 

 behind the head is a smaller middle 

 piece which is the chief cytoplasmic 

 portion of the cell; the cytoplasm is 

 really continued as a very thin envelope 

 over the head, at the anterior end of 

 which it is usually produced as a sharp- 

 ened perforating or attaching organ 

 called the acrosome or perforatorium. 

 In some spermatozoa (e.g., some Mam- 

 malia) the head is connected with the 

 middle piece by an intermediate section 

 called the neck (Fig. 51). The middle 

 piece is quite highly differentiated. It 

 contains the centrosomal structures of 

 the spermatozoon, and its center is oc- 

 cupied by the proximal portion of a 

 kinoplasmic structure, the axial fila- 

 ment. Surrounding this are frequently 

 one or more differentiated layers, and 

 often a spirally wound thread; the 

 whole is covered with a dense outer 

 sheath. In some instances (toad) the 

 centrosome is said to be included in the 

 region of the head piece. Extending 

 posteriorly from the middle piece is a 

 long flagellum or tail, in some species 

 flattened and provided with a fin-like 

 undulatory membrane (Fig. 52, L). 



