EXPLANATION OF PLATE X. 



Above Stages of the conversion of the spermatid into the spermatozoon in 

 the Hemipteran Euschistus, after MONTGOMERY ( 1 9 1 1 a), (a] In the centre, 

 nucleus with centrosome and axial filament ; below, mitochondrial body; 

 to the left, the "sphere." (b] The mitochondrial body is beginning to be 

 drawn out along the growing axial filament ; the sphere shows signs of 

 division, (f), (d) Further stages of the same process. (e), (f) The 

 sphere has divided, and part of it gives rise to the acrosome. (g) Head 

 of nearly mature spermatozoon. 



Middle Part of testicular tubule of Rat, showing Sertoli cells to which bundles 

 of spermatozoa are attached. From KORSCHELT and HEIDER, after LEN- 

 HOSSEK. 



Below So-called apyrene spermatozoon of Permetus, after KUSCHAKEWITSCH. 

 The cell-body is filled with "albumen-spheres" which are deposited 

 after the chromatin of the spermatid has completely degenerated. The 

 bundle of axial filaments (the full length of which is not represented) 

 grows out from numerous centrosomes arising by multiplication of the 

 spermatid centrosome. 



