22 



HISTOLOGY 



Spermatogonia 



lower down in the lobe, since the cysts form at the apex and gradually 

 move downward. At the apex, according to Davis, there is an apical 

 cell which is surrounded by young sexual cells known as spermatogonia 

 (Fig. 17, a). The spermatogonia move away from the apical cell, and 

 each becomes enclosed in a cyst-wall derived from the surrounding 

 tissue. Within the cysts thus formed, the spermatogonia multiply, and 

 the cysts in the upper part of the lobe are filled with spermatogonia 

 (Fig. 17, b). After repeated divisions the spermatogonia pass through a 

 period of growth, accompanied by a rearrangement of their nuclear con- 

 tents. The large cells with characteristic nuclei which are thus produced, 

 are known as primary spermatocytes. They fill the cysts further down 

 in the lobe (Fig. 17, c). Each primary spermatocyte divides into two 



secondary spermatocytes, and 

 each of these divides into 

 two spermatids, after which 

 no further cell division is 

 possible until fertilization 

 takes place. But each sper- 

 matid becomes transformed 

 from a round cell into a linear 

 body with a whip-like tail, 

 and is then capable of inde- 

 pendent motion. Since in 

 this form these cells were 

 once thought to be parasitic 

 animals living in the sper- 

 matic fluid, they received the 

 name spermatozoa, which they 

 still retain. 1 Cysts contain- 

 ing spermatozoa occur near the outlet of the lobe, or if the grasshoppers 

 are collected late in the season, they may be found throughout most of the 

 testis. Specimens from young grasshoppers, in which the spermatocyte 

 divisions are abundant, are more desirable, even though no spermatozoa 

 have become fully developed. 



The succession of cell divisions described in the preceding paragraph 

 is shown in tabular form in Fig. 18. Except for the number of chromo- 

 somes within the various cells, this diagram is quite as applicable to man 

 as to the grasshopper. In this figure, however, only two spermatogonial 

 divisions have been included. The number of times which the spermato- 

 gonia may divide before becoming spermatocytes is considerable and 



1 It has been proposed to substitute the term spermium for spermatozoon; and consequently 

 spermiocyte, spermid, etc., for spermatocyte and spermatid. The secondary spermatocytes are 

 sometimes called praespermatids or praespermids; but these changes in names are of questionable 

 value 



Secondary Spermatocytes 



Spermatozoa 



FIG. 1 8. DIAGRAM OF THE CELL DIVISIONS IN SPERMATO- 

 GENESIS. The figures indicate the number of chromo- 

 somes found in the cells of certain grasshoppers. 



