vii] MITOCHONDRIA 95 



mitochondria already shortly referred to in Chapter II. 

 They were first observed in spermatocytes and spermatids, 

 but have since been found in many other cells of various 

 animals, especially in the embryo.' To see them well the 

 tissue must be preserved in a special manner, the most 

 important point being that the fixative should contain no 

 acetic acid. They stain well, but somewhat capriciously, with 

 HEIDENHAIN'S iron-haematoxylin, and particularly with 

 BENDA'S process. In the spermatocyte, as the cell enlarges, 

 the mitochondrial bodies increase in size, and are usually 

 described as becoming definite threads of staining substance 

 which frequently take the form of loops or rings. In both 

 the spermatocyte divisions they may appear to be drawn 

 out parallel with the spindle, in a somewhat irregular 

 manner, and as the cell divides they are separated about 

 equally into the daughter cells. In the young spermatid 

 they unite to form a fairly compact mass near the nucleus 

 at the side of the cell at which the tail will grow out 1 . In 

 the stages for which GATENBY has proposed the name 

 spermateleosis, that is, during the final development of the 

 spermatozoon from the spermatid by the outgrowth of the 

 cytoplasm along the axial filament (sometimes also called 

 "spermiogenesis"), the mitochondrial mass becomes drawn 

 out so as to form an elongated sheath enclosing the filament. 

 Its final fate is uncertain, but will be shortly referred to 

 below. 



In testes fixed by the usual methods (for example 

 Flemming's fluid, alcohol-sublimate acetic mixtures, etc.) 

 designed especially for giving clear figures of the nucleus 



1 This mitochondrial mass ("mitosome") constitutes the "Nebenkern" of 

 some authors, but as the word has been used to designate the remains of the 

 division-spindle (" SpindelrestkOrper," "spindle-bridge"), the "idiozome" (or 

 "sphere") and other cell-structures, it is now dropping out of use. 



