338 HISTOLOGY 



filament with its surrounding membrane; and the end piece (10 /") is 

 a prolongation of the filament. When the spermatozoa become free they 

 float in the albuminous fluid secreted in small quantity by the tubules of 

 the testis. They pass through the straight tubules and rete to the epi- 

 didymis, in which they accumulate, and where they first become motile. 

 Their motility is greater, however, in the seminal fluid, which is a mixture 

 of the products of the epididymis, seminal vesicles, prostate and bulbo- 

 urethral glands. By an undulating movement of the tail, the head is 

 propelled forward, always being directed against such a current as is made 

 by cilia, at a rate of | of an inch in a minute. Water inhibits the motion, 

 which is favored by alkaline fluids; it occurs also in those faintly acid. 

 For three days after death spermatozoa may retain their activity in the 

 seminal passages; in the female urogenital tract they may live a week 

 or more. In addition to normal spermatozoa, giant forms, and some 

 with two heads or two tails occur, but these are probably functionless 

 abnormalities. The production of spermatozoa, beginning at puberty, 

 continues throughout life, but with advancing age the rate diminishes. 

 Since about 60,000 spermatozoa occur in a cubic millimeter of seminal 

 fluid, it has been estimated that 340 billions are produced in a lifetime. 



The discovery of spermatozoa was reported to the Royal Society of London, in 1677 

 by Leeuwenhoek. They were first seen by Dr. Ham, "a man of singular modesty," 

 to whom Leeuwenhoek gives full credit for the discovery in his letters to the Royal 

 Society. He wrote as follows: 



"This discerning youth visited me and brought with him, in a small glass vial, 

 seminal fluid from a man who had cohabited with a diseased woman; and he stated that 

 after some minutes when the fluid had become so attenuate that it could be put in a 

 slender glass tube, he had seen living animalcules in it, which he thought were pro- 

 duced by some putrefaction. He added that those animalcules seemed to him to be 

 provided with tails, and that they did not survive the space of twenty-four hours. 

 Moreover he declared that when terebinth had been given to the patient internally, the 

 animalcules appeared to be dead. 



"I poured this material in a glass tube and examined it in the presence of Dr. Ham, 

 and saw some live animalcules in it. But when after two or three hours, I examined 

 the material more carefully, by myself, I saw that all the animalcules were dead." 



Leeuwenhoek diligently pursued the study of these animalcules, and found them in 

 enormous numbers in the semen of insects, fishes, birds and quadrupeds. He estimated 

 that there were 150,000,000,000 in the milt of one fish, or more than ten times the num- 

 ber of men then living (13,385,000,000 homines in orbe terrarum). Leeuwenhoek be- 

 lieved that the animalcules were of two sexes, and that the egg consisted of a fluid in 

 which they swam about and developed. To some it seemed not unreasonable that new 

 individuals should be enclosed in the spermatozoa, like an insect in its chrysalis, and 

 Dalenpatius (1699) thought that he could observe them. As quoted by Vallisneri, he 

 wrote as follows, illustrating his account with the figure here reproduced (Fig. 338). 



"We have seen some animalcules having just the form of tadpoles such as are found 

 in brooks and muddy bogs in the month of May. The tail is four or five times as long, 

 as the body. They move with wonderful rapidity and by the strokes of their tails pro- 



