300 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



filiform. I was not able by the use of Delafield's hseraatoxylin and 

 picric acid to differentiate a middle piece in the adult spermatozoon, nor 

 have I given special attention to studying the ultimate structure of this 

 element. 



As the egg on being deposited passes through the hermaphroditic duct, 

 the spermatozoon, it must be assumed, approaches and penetrates it (Plate 

 9, Fig. 60 ; Plate 8, Fig. 56), the tail being lost in the act. While the egg 

 remains in the hermaphroditic duct, no change is noticeable in the sperm 

 head, but immediately after deposition the head becomes much enlarged. 

 Finely granular cytoplasm collects around it, and on one side of it there 

 appear a few coarse granules ; it was impossible, however, to trace the 

 origin of these to any particular part of the spermatozoon. They persist 

 for a considerable time, but neither they nor anything resembling a sperm 

 sphere or sperm aster become permanently associated with the sperm head 

 during its migration in the egg. The sperm head increases in size and 

 becomes more or less elliptical in outline, though one end is usually 

 more pointed than the other (Plate 8, Fig. 57 ; Plate 9, Fig. 64). It is 

 vei'y difficult, however, to say with any certainty which end of the sperm 

 head leads during its changes in position. While the" egg remains in the 

 hermaphroditic duct, the sperm head usually lies near the periphery with 

 its long axis at right angles to the radius of the egg ; when migration 

 begins, one end turns toward the deeper aster of the maturation figure. 

 In some cases (Figs. 56, 62) tlie anterior end seemed to lead ; in other 

 cases the reverse was true. In still other instances the sperm head 

 remained near the periphery of the egg until it had assumed a spherical 

 form, the egg having meantime passed into the anaphase of the second 

 maturation. While the sperm head is migrating through the deutoplasm, 

 its outline shows all gradations of form from that of a much elongated 

 oval to that of a sphere. The sperm head may remain solid and homo- 

 geneous until it has penetrated deep into the egg (Plate 8, Fig. 57), — until 

 the metaphase or even the anaphase of the second maturation (Plate 9, 

 Fig. 61) ; but it may show signs of vacuolation as early as the metaphase 

 of the first maturation. The first evidence of vacuolation results from 

 the central region not staining as densely as the rest of the head. The 

 vacuoles are at first very small, aud as many as six have been observed. 

 There may be a central vacuole which increases in size, or several inde- 

 pendent vacuoles may unite to form a large one (Figs. 63, 64). There 

 is, therefore, no very precise correlation between the times of migration 

 and vacuolation, nor between the metamorphosis of the sperm head and 

 the maturation of the egg. The sperm head shown in Figure 61 is 



