BEHAVIOR OF THE GAMETES 231 



achieved, namely, contact of a single sperm with an egg, but from the view- 

 point of sperm survival it may appear as waste and caprice. This fact is espe- 

 cially true in those forms utilizing fertilization where only one or a very few 

 eggs are fertilized. It has been shown by Walton ('27) in experiments dealing 

 with artificial insemination in the rabbit, when dilution of the sperm is such 

 that the number falls below 3,000 to 4,000 per cc, fertilization does not take 

 place. Recent observations by Farris ('49) on the human suggest that num- 

 bers of sperm below 80,000,000 per cc. are precarious when conception is 

 the end to be achieved. (For the total number of sperm ejaculated by certain 

 males during a single copulation, see Chap. 1.) Although exceedingly large 

 numbers of sperm are deposited in the posterior area of the female repro- 

 ductive tract, the number becomes less and less as the ovarian end of the 

 duct is reached. The ability of effective sperm transport within the female 

 tract probably varies considerably in different species and with different fe- 

 males in the same species. The rat and the dog appear to be more efficient 

 in this respect than the rabbit. 



The relation of sperm numbers to the efficiency of the fertilization process 

 is not to be considered merely as a mechanical hit and miss device, whereby 

 the presence of a greater number of sperm may assure an accurate "hit" or 

 sperm-egg collision (Rothschild, Lord, and Swann, '51). Hammond ('34) 

 has shown in the rabbit that fertilization is not effected by the few sperm 

 which reach the region of the egg first, but by the later aggregations of num- 

 bers of sperm. The work on hyaluronidase mentioned on page 229 suggests 

 strongly that one object of the excess sperm is to transport hyaluronidase to 

 the vicinity of the egg. The presence of this enzyme close to the egg possibly 

 facilitates the passage through the cells of the corona radiata and also through 

 the zona pellucida of the single sperm which makes contact with the egg in 

 the process of fertilization (Tyler, '48). The general result should be regarded 

 as the working of a cooperative enterprise, where many sperm aid in the dis- 

 solution of the interference in order that one sperm may reach the egg's surface. 



3) Influences of the Seminal Plasma in Effecting Sperm Contact with the 

 Egg. The importance of the seminal plasma (i.e., the fluid part of the semen; 

 see Chap. 1) cannot be overestimated (Mann, '49). It is, to a great extent, 

 the natural environment and at the same time the nutritive medium for the 

 sperm during the transport from the male ducts through the external medium 

 or within the lower region of the female genital tract. Its functions may be 

 stated as follows: 



(1) It increases the motiUty of the sperm; 



(2) it has a high buffering capacity, which protects the sperm from in- 

 jurious acids or other injurious substances; and 



(3) it is a vehicle for nutritive substances, such as fructose, vitamin C, 

 and the B complex which provide nourishment for the sperm. 



