EXPLANATION OF PLATE XI. 



Mitochondria in the spermatogenesis of Lepidoptera, from GATENBY. (Repro- 

 duced by permission from Quart. Journ. Micr. Sci. LXII. 19 17, Plates 23, 25.) 

 i 5. Smerinthits popitli ; 6, Euchelia jacobaeae. 



1. Spermatogonium with mitochondrial granules (MD), around nuclear mem- 

 brane. 



2. Primary spermatocyte with mitochondrial vesicles (MD}, acroblasts (AB), 

 and two centrosomes (C), with double axial filaments. 



3. First spermatocyte division. 



4. Spermatid showing mitochondrial vesicles coalescing to form the mitosome. 

 j. More advanced spermatid. The mitosome has assumed the form of a 



spiral thread around the axial filament (FL). The acroblasts are applied 

 to the nucleus as vesicles. 



6. Head of a later spermatid, well advanced towards a mature spermatozoon. 

 The acroblast vesicles have coalesced to form the acrosome (AG]. 



Explanation of lettering. 



AB, acroblast ; AG, acrosome ; AXF, axial filament ; C 1 , proximal centrosome ; 

 C' 2 , distal centrosome of spermatid, which passes down into the tail; CO, 

 non-staining portion of mitosome ; FL, axial filament ; M, micromitosome ; 

 MD, mitochondria ; N, nucleus ; SP, mitochondrial spireme ; XT, 

 outline of neighbouring cells. 



