232 KIYOSHI MASUI. 



which iu a Liter stage ssem to increase (Figs. 119, 120). The augmentation 

 of them in this period was reported by Duesbebg ('08 b) in the rat and by 

 Jordan ('12) in opossum. 



Later on the main portion of the cytopLism moves backwards, assuming 

 a rounded body, and comes to be pkced enth-ely in front of the nucleus whicli 

 now becomes more and more elongated, till it finally assumes its position as 

 the head of ripe spermatozoon (Figs. 121, 123). Duiing these changes the 

 mitochondi-ial granules gradually collect in several groups and finally Ijecome 

 an-anged around the axial filament, while the " Schwanzmanschette " entirely 

 disappears (Figs. 122-123). 



In the middle piece of the ripe spermatozoa found in the tubule, about 

 twenty fom- large gi-anules can be counted airauged in two rows along the 

 side of the axial filament (Figs. 124-125). From what is skited above it is 

 clear that these granules are formed by the aggi-egatiou of the small 

 mitochondiial gi-anules. 



General Considerations. 



I. The ChKOMOSOMES of the SPERSrATOGONIA. 



Number of chromosomes m rodents : — As to the numljer of chromosomes 

 in the rodents there is a wide difference in opinion among the investigators. 



In the matm-ation of the egg of the mouse, SoBOTrA ('95) and Kikkhah 

 ('07) reported twelve chromosomes, while Long and Mark ('11) counted 

 twenty chromosomes, in both the maturation divisions. YocüM ('17) i-eportsd 

 twenty chromosomes as the reduced number in the male germ cells of the mouse. 



But, as far as I am awai-e, none af the investigators gave the positive 

 diploid number of chromosomes in the mouse. In the rat Duesbebg ('08 a) 

 reported twelve chromosomes as the reduced number. Recently Allen ('18) 

 has coimted thirty seven chromosomes in the spermatogoniii of the rat, nine- 

 teen in the fii-st reduction division. 



In the rabbit Wjniw.vbter ('00) foimd that the somatic chromc»omes 

 vary from thirty six to eighty. Bachhuber ('16) repoiied twenty two chromo- 

 somes as the diploid numbar and twelve as the reduced number in ths male 

 germ cells of the rabbit. Stevens ('11) counted fifty six cJiromosomes in the 



