SPERMATOGENESIS OF SCUTIGERA FORCEPS. 159 



taining the largest number of cells, all are in practically the same 

 stage of development, and is further supported by the fact that, 

 almost without exception, where cysts contain the smaller num- 

 bers, several composed of cells in practically the same stage of 

 development are to be found in the same region of the testis. 



The spermatogonia are small spherical cells, averaging about 

 eleven or twelve micra in diameter. During the late prophase 

 of the last spermatogonial division, the chromosomes lie in the 

 clear nuclear area at the center of the cell (Fig. i). These 

 chromosomes, with the exception of one which stains more 

 darkly than the others, present a dense granular appearance 

 when stained with Heidenhain's iron-hfematoxylin. The total 

 number of these chromosomes is constantly thirty-seven (Fig. i), 

 which, if the accessory chromosome is excluded in both cases, is 

 twice the number found in the spermatocytes, showing that this 

 element remains distinct throughout the whole period of sper- 

 matogenesis. 



During the metaphase of the last spermatogonial division the 

 chromosomes may be seen lying in the equatorial plate, so placed 

 as to form a ring ; but owing to the minute size of the compo- 

 nent elements and their close proximity to one another, they ap- 

 pear rather as a solid mass than as separate chromosomes (Fig. 

 2). When viewed in cross section, they present the appearance 

 either of a plate densely crowded on the outside, with separate 

 chromosomes scattered throughout the middle, or of a ring. 

 The centrosomes may be seen lying in the cytoplasm at some 

 distance from the cell-wall and at this period appear as minute 

 particles staining an intense black with the iron-haematoxylin. 

 Emerging from these points and directed towards the cell-wall 

 are astral rays which are so fine and delicate as to appear mere 

 elongations in the reticulum of the cytoplasm, rather than defi- 

 nite structures. The spindle-fibers, however, stain intensely and 

 may be seen as separate threads connecting the chromosomes 

 with the centrosomes. 



In the early telophase, after the two groups of chromosomes 

 have moved to opposite ends of the cell, the spindle threads, still 

 staining intensely, lie stretched between these two masses, while 

 the centrosomes have become lost (apparently) among the chro- 



