HUMAN SPERMATOGENESIS: A STUDY OF INHERITANCE. 17 



more frequently in several fragments as indicated in figs. 90, 99, 102, and usually 

 the anterior region of the head is the first to become freed from it. Many of 

 the spermatozoa within the epididymis still possess masses of cytoplasm, and 

 occasionally some of those in the vas deferens. In the fully matured spermato- 

 zoon (fig. 109) the only cytoplasm would seem to be enveloped around the chon- 

 drial mantle. The abstricted cytoplasmic masses are easily recognized within 

 the lumen of the seminiferous tubules and in the epididymis. 



There remains to be noted only the mitochondrial mantle. In the sperma- 

 tocytes and spermatids no mitochondria are observable, and they had probably 

 been dissolved by the fixatives. In fig. 98, PL IV, is represented an abnormal 

 in i mature spermatozoon with two axial filaments, and around each of the latter 

 an irregulsjl coil of dark-staining substance (Mit.) that seems to be an early stage 

 of the mitochondrial mantle. It is to be noted that while these exhibit a certain 

 spiral disposition, there is no indication that each is a continuous spiral. The 

 mitochondrial mantle of the mature spermatozoa (Mit., figs. 109-112, 114, 115) 

 is of variable length, but always longer than the head, lies immediately behind 

 the neck, and generally appears as a dense mass without differentiation. But in 

 one case (fig. 107) it was clearly seen to compose a hollow cylinder around the 

 axial filament and to show a somewhat granular structure. 



3. The Ripe Spermatozoa. 



These are shown in figs. 107-115, from the vas deferens (figs. 108, 110, 111, 



seen from edge) and their structure has been elucidated by the preceding account 



of their histogenesis. The head is composed of two parts, sometimes (rather 



rarely) demarcated by slight annular girdle or groove; an anterior part which 



contains one or several droplets of karyolymph, and which appears lighter by 



reason of its being more flattened; and a posterior thicker part that is entirely 



dense. Next follows the anterior portion (fig. 115, c.p.) of the proximal centriole, 



the clear region of the neck, the posterior portion of the proximal centriole 



(c.p. 2), the mitochondrial mantle (Mit.), the principal part of the tail, and 



finally the terminal filament (figs. 109, 114). No trace of the distal (ring) 



centriole can be found, and frequently the parts of the proximal centriole are 



not apparent. No cytoplasm was observable in the head and neck region; in 



in the remainder it forms a mesh within and around the mitochondrial mantle 



(fig. 107). It could not be observed that the mitochondrial mantle composes a 

 spiral thread. 



The heads of the mature sperm from the vas deferens vary remarkably in 

 volume, and figs. 113 and 112 show the largest and smallest found. To determine 

 the nature of this variation the heads of 100 mature spermatozoa, chosen at 

 random, were carefully drawn to the same scale, the precaution being taken to 

 draw only such as lay exactly in the plane of the section. The drawings were 

 then measured in millimeters, and showed a range in length of the heads from 

 10 mm. to 27 mm. Plotting the measurements according to size they are seen 



2 JOURN. ACAD. NAT. SCI. PHILA., VOL. XV. 



