REPROD UCTION. 



883 



claims the number of chromosomes in the chromatic substance after matura- 

 tion to be eight. 



The middle-piece (m) is a short, cytoplasmic rod, probably containing a cen- 

 trosome. The tail (t) is a delicate filiform, apparently cytoplasmic structure, 

 and analogous to a single cilium of a ciliated cell. The tail is tipped by an 

 excessively fine, short filament, the end-piece (e). The most 

 abundant of the solid chemical constituents of the spermato- 

 zoon is nuclein, probably in the form of nucleic acid, which 

 is found in the head. Other constituents are proteids, prota- 

 mine, lecithin, cholesterin, and fat. 



The structure and power of movement of the spermatozoon 

 plainly show it to be adapted to activity. It is not burdened 

 by the presence of food-substance within its protoplasm. It 

 is the active element in fertilization ; it seeks the ovum, and 

 it is modified from the form of the typical cell for the special 

 purpose of fertilization. The nucleus is the fertilizing agent- 

 The head is plainly fitted for facilitating entrance into the 

 ovum. The tail is a locomotor organ capable of spontaneous 

 movements, and, after expulsion of the semen, it propels the 

 cell, head forward, through the fluid in which it lies. The 

 movement is a complex one, and is effected by the lashing 

 of the tail from side to side, accompanied by a rotary move- 

 ment about the longitudinal axis. The rate of movement has .. FIG. 305. Human 

 been variouslv estimated at from 1.2 to 3.6 millimeters in the ^ rma * oz ? (after 



jtvciziusj . A t sperm- 



minute. Toward heat, cold, and chemical agents spermatozoa atozoonseenen/ace; 



i , -1.1 .. , j n h, head; m, middle- 



behave like ciliated cells. piece . , tail . e> end . 



Ripe spermatozoa appear to be capable of living for months P iece = B > c > se en 



.... , . , , , 111 from the side. 



within the male genital passages, where they are probably 

 quiescent. Outside of the body they have been kept alive and in motion for 

 forty-eight hours. It is not certain how long they may remain alive within 

 the genital passages of the human female. They have been found in the os 

 uteri and capable of movement more than eight days after their discharge. It 

 seems not improbable that within the female organs their environment is favor- 

 able to a somewhat prolonged existence. In this connection it is of interest to 

 know that spermatozoa capable of fertilizing have been known to live within 

 the receptaculum seminis of a queen bee for three years. 



Sperrnat *>a are produced in large numbers. Upon the basis of observa- 

 tions in several individuals, Lode 1 computes the average production per week 

 as 226,257,000, and in the period of thirty years from twenty-five to fifty-five 

 years of age the total production as 339,385,500,000. This excessive produc- 

 tion is an adaptation by nature that serves as a compensation for the small 

 size of the cells and the small chance of every cell finding an ovum. With- 

 out large numbers fertilization would not be ensured and the continuance of 

 the species would be endangered. 



1 A. Lode : Pftiiger's Archivjur die gesammte Physiologie, 1., 1891. 



