GAMETOGENESIS OF SACCOCIRRUS 37 



sperm is the only part which is meticulously guarded during 

 spermatogenesis of all animals. 



That the male and female pronuclei contain the same number 

 of chromosomes (leaving out the special x or y chromosomes) 

 is a notorious fact. The sperm never contains as many mito- 

 chondrial granules as the egg, and in only one case (A s c a r i s 

 megalocephala (32)) has it been shown that at the time 

 of fusion of the o^ and ? pronuclei, the number of mito- 

 chondria of the a^ gamete are about the same as those of the 

 5 . The above comparisons show conclusively that of all the 

 cell elements the chromosome is the only one whose behaviour 

 is precise and coincident with the expected conduct of bodies 

 directly engaged in the processes of heredity, the results of 

 which, as breeding experiments show, are often of previously 

 calculable exactitude. 



As direct bearers of any important or precise factors of 

 heredity, the Golgi body and mitochondria appear to be ruled 

 out by their inexact and variable behaviour in the germ-cell 

 cycle. The chromosomes, and the chromosomes alone, fulfil 

 the necessary conditions. 



11. Summary. 

 Spermatogenesis. 



1. The spermatogonium is of the usual type, containing both 

 mitochondria and Golgi apparatus (PL 1, fig. 7). 



2. The spermatocyte contains the same inclusions as the 

 spermatogonium, but in addition there is to be found, in 

 a large number of cases, a group of granules generally lying 

 near the Golgi elements and giving the microchemical reactions 

 of true yolk, i. e. turning greenish yellow in chrome-osmium 

 fixatives, not staining in haematoxylin or acid fuchsin, and 

 generally dissolved out by strong lipoid solvents (PI. 1, fig. 1, y). 



3. Nurse-cells often accompany groups of spermatogonia. 

 The nurse-cells contain large quantities of yellowish yolk, 

 as well as fuchsinophil bodies, possibly mitochondrial in 

 nature (PI. 1, fig. 1, yc). 



