Blackman. — Spsrniatogenesis of Scolopendra. 



PLATE 7. 



Late stages in the metamorphosis of the spermatid. Figures 107, 108, and 115-120 

 are magnified 1747 diameters : all others, 1280 diameters. 



Fig. 102. Later stage in the elongation of the nucleus. This is the period during 

 which the chromatin is in its most diffuse condition, for only a very 

 little of it stains in the ordinary manner, while the rest of the nucleus 

 assumes a reddish gray color. At this time the two lateral centro- 

 somes again become distinguishable. They lie in the nucleus and 

 are connected by fibres with the end knob of the axial filament. 



Fig. 103. Spermatid of the small type at about the same stage as that of Figure 

 102. The centrosomes are much more distinct than in the other type, 

 Figure 102. Cells similar to this are very numerous. 



Fig. 104. Spermatids slightly older than that of Figure 102. The chromatin is 

 regaining its affinity for nuclear stains. Centrosomes still very easily 

 distinguished. At the juncture of acrosome and nucleus a clear vacu- 

 ole lias appeared. 



Fig. 105. Spermatid of the small type of about the same stage as that of Figure 104. 



Fig. 106. The chromatin again stains deeply, and the whole of the nucleus except 

 a small portion appears homogeneous. The acrosome has become 

 condensed and now stains gray. 



Figs. 107, 108. The nuclear portion of cells of the same stage as that shown in 

 Figure 106 under higher magnification, showing the presence of a 

 large vacuole at the anterior end of the head. In Figure 108 the 

 lateral centrosomes are seen inside the head surrounded by a lighter 

 area. The end knob appears in both figures. 



Fig. 109. The nucleus is further elongated. The acrosome is also elongating, a 

 projection being thrust out from one side of it near its anterior end. 



Figs. 110-112. The nucleus and acrosome continue to elongate. At this stage nu- 

 merous small vacuoles, or one large one, are often seen in the nucleus. 

 In Figure 111 the three centrosomes are plainly seen, two within the 

 nucleus and one forming the end knob of the axial filament. 



Fig. 113. Cross sections of young spermatozoa of the stage of Figures 110-112, 

 showing a large central vacuole in the head region. The diameter 

 of the cell in the region of the axial filament is much less than in the 

 head region. 



Fig. 114. Later stage, showing the beginning of the spiral condition of the head. 



Fig. 115. Portions of the head region of a nearly mature spermatozoon demon- 

 strating the nature of the spiral ; a, cross sections, showing the central 

 clear region and the outer dark region of the head with a thickening 

 which corresponds to the spiral ridge ; b, longitudinal optical section, 

 showing same structure from another point of view ; c, surface view. 



Figs. 116-119. Nearly mature spermatozoa, showing the inner lighter area of the 

 head, the centrosomes and their relation to both head and axial 

 filament. 



Fig. 120. Portion of the head region of mature spermatoon, showing centrosomes. 



Fig. 121. Entire head and axial filament of a mature spermatozoon as seen in the 

 testis. The length of head and acrosome is 260 micra. Only one 

 centrosome is seen, owing to the direction from which the object is 

 viewed. 



