to recognize it (Figs. 28 to 32). A clear space surrounding 

 the nucleus Is also seen in these figures. The spermatid as 

 it appears In Pig. 32 rests for a conslderahle period hefore 

 any change towards the formation of the sperm is observed. The 

 boundaries "between the cytoplasm of the different cells dis- 

 appear and the nuclei come to lie in a sort of Plasmodium. 



7. T he transformation of the spermatid into the sperm . 



In serial sections of a single tuhule we may trace every 

 stage in the transformation of the spermatid into the sperm, 

 and since the two ends of the series are in opposite ends of 

 the tubule and the intermediate stages lie in serial order 

 between these ends we may use the position of a seminal ele- 

 ment in the tubule as a criterion for determining its relative 

 stage in the course of development. The first evident step in 

 the transformation of the spermatid is the appearance of 

 vacuoles in the cytoplasm next to the nucleus. These are at 

 first small but by coalescing they soon form a large, clear 

 vacuole on one side of the nucleus (Figs. 3J5 to 38). Some- 

 times it appears that the vacuole may have arisen by the nu- 

 cleus settling to one side of the clear space surrounding it 

 in Pig* 31. The nuclei, each with its accompanying vacuole, 

 now lie in a common mass of cytoplasm. In the further develop- 

 ment of these cells there are three parts that must be con- 

 stantly borne in mind, viz., the nucleus, the vacuole (here- 

 after called the capsule) and the cytoplasm. We shall take 

 up certain stages in the differentiation of these three 



