THE fu'ERlIATUGEXESK OF DOMESTIC II VMMAT.S. 209 



Observations. 



I. The Speiimatugosia. 



A. The speriDatogonia iu the mouse. 



As I hnve idready dcscrilnxl in cittle, in tlio testes of mature aniiuals 

 several sizes of spermatogoui.'il cells can bo clistiuguishocl (Figs. 4, 14'. This 

 diftevence iu size seems to indicate the generations of the spermatogonia, the 

 l.vrger cells being earlier in generation tlian tho smaller ones. It is, liowevev, 

 a difliciilt matter to det*ir;niuo accuratjly tho number of generations of the 

 S{)ermat(3gonia. 



The resting nucleus of every spermatogonial cell usually contains one 

 nncleolos and several clu'omatin masses which usually lie on the nuclear 

 membrane and on the linin threads (Figs. 126, 127). The nucleolus gives 

 an :ipi;earance of gi'anular construction, since a small amoimt of chromatin 

 gi-aunles are gathered on the surface of it (Figs. 126, 127). Thus it is 

 difficult to distinguish the nucleolus iu the preparations stained with irou- 

 haMnatt)xylin (Figs. 1, 2), while this can clearly be seen in those sku'ned 

 with AuEUBACu's method (Fig. 127). 



The nucleolus giadiuiUy disappears in the prophase, leaving a plastiu 

 remnant behind ; thus it is clear that there is no connection between this 

 body and the sex-chromosomes which are foimd iu tho prophase of tho first 

 reduction division. The chromatin granules later begin to arrange themselves 

 along .short threads which coiTespi:>nd tj tho chromatin spiremes iu otlier 

 .•luimals (Fig. 2). The chromatin threads now become gradually denser and 

 thicker imtil the granular appearance is entirely lost to view (Fig. 3)- 

 As stated, above, tho nucleolus usimlly disappears at the late prophase but 

 it remains sometimes among the chromosomes in the early metaphase (Fig. 

 127). This, however, can not be recognized, when the cluromosomes are 

 an'anged radially around the central space in the metaphase. 



As the mitotic figures arc rare in mammalian tissues compared with 

 those of the lower animals, in the determination of the number of chromosomes 

 the method of using thick sections is, in my experience, preferable to the 

 smear metlicxl. As Montgomery ('10) stilted, it is tinoe thfit the difficulty in 

 determining the uiuuber of chromosomes increases in geometrical ratio with 



