DAVIS: SPERMATOGENESIS. 113 



tid. The further changes consist chiefly in a still greater elongation 

 of the head until it becomes several times the length shown in Figure 

 223 and correspondingly smaller in diameter. 



Spermatids which are much larger than normal ones and contain 

 two or more centrosomes are occasionally met with. Figure 217 

 shows one of these abnormal spermatids with four centrosomes, each 

 of which has an axial filament connected with it. The number of 

 such abnormal spermatids varies in different indi^'iduals, although 

 they are never very common. Similar abnormal spermatids have 

 been described by Paulmier ('99) and others. 



I have not found e\idence of the degeneration of spermatids or 

 spermatozoa, except in rare cases. 



Inasmuch as only one-half of the spermatids contain the monosome, 

 and as there is no evidence that the monosome is extruded from the 

 nucleus during the metamorphosis or that any considerable number 

 of the spermatitls degenerate, it follows that the mature spermatozoa 

 are dimorphic, even though there is no recognizable difference between 

 them, — half of them containing the substance of the monosome, the 

 other half beino- without that substance. 



'& 



B. Steiroxys trilineata. 



In the resting spermatids (Plate 8, Figs. 200-203) the autosomes, 

 have become broken down into granules distributed through the nu- 

 cleus, but the monosome retains its compact form and shows the 

 staining reactions characteristic of dividing chromosomes. It forms 

 a lenticular body closely applied to the inner surface of the nuclear 

 membrane and, on account of its large size and staining reactions, is a 

 very conspicuous element of the spermatids. Figures 200 and 202 

 show resting spermatids which contain the monosome, while Figures 

 201 and 203 show others in the same stage in which this element is 

 lacking. Ljing near the nucleus, on the side covered with the greatest 

 amount of c}i:oplasm, is a rounded homogeneous body staining deeply 

 with Bordeaux; for convenience I shall call this the Nebenkern, with- 

 out impl\ing anything in regard to its homologies. Often a less 

 deeply staining body can be distinguished closely applied to the nu- 

 clear membrane near the Nebenkern (Fig. 203). This body is usually 

 difficult to distinguish from the surrounding cytoplasm, but is prob- 

 ably of universal occurrence. During the telophase of the second 

 maturation division the cytoplasmic structures are very indistinct, so 

 that I have been unable to determine the origin of the Nebenkern and 



