ioo CYTOPLASMIC STRUCTURES [CH. 



behind the nucleus in the mature spermatozoon. As the 

 tail grows out and the spermatid elongates, the idiozome 

 gradually travels forward, so that by the time when the 

 nucleus is being converted into the head of the spermato- 

 zoon the idiozome is in front of it and in close contact with 

 its anterior pole, where it becomes concentrated and pointed 

 in shape and gives rise to the apical body or acrosome. 

 Usually the whole idiozome is described as being converted 

 into the acrosome, but in Euschistus MONTGOMERY finds 

 that it divides into two parts, one of which travels forward 

 to form the acrosome while the other remains behind the 

 nucleus and seems eventually to disappear (PL X, af). 



In Lepidoptera, however, GATENBY (1917 a) has given an 

 entirely different account of the origin of the acrosome. In 

 the primary spermatocytes he finds deeply stained rod-like 

 bodies which from their subsequent fate he names aero- 

 blasts ; they are usually curved with their concave sides 

 lying toward the nucleus, and lying in parts of the cyto- 

 plasm free of mitochondria. Their number varies somewhat 

 in different species. In the spermatocyte divisions they be- 

 come distributed to the daughter cells, and their movements 

 appear to be more definitely controlled by the astral rays 

 than those of the mitochondria. In the spermatid they be- 

 come first hemispherical, with a non-staining centre, and 

 then round hollow vesicles. The vesicles, which in Smerin- 

 thuspopuli are from three to five in number in the spermatid, 

 arrange themselves around the nucleus and then become 

 adherent to it. At the point at which each vesicle touches 

 the nucleus a staining granule is formed, and as the sperma- 

 tid nucleus contracts to form the head of the spermatozoon 

 the acroblast vesicles coalesce, and the contained granules 

 unite to form a single body which gives rise to the acrosome 

 (PI. XI, 3-6 AB, AG\ 



