GENERAL BIOLOGY 



"Light could probably be thrown on this matter by some such ex- 

 periments as follow : keep a number of worms, each in a separate flower- 

 pot, from infancy to maturity; kill a few and examine the contents of 

 their spermathecae (it is conceivable that a worm may be able to pass 

 spermatozoa into its own spermathecae) ; allow remainder to mate once,, 

 note if cocoons are deposited ; kill some and examine contents of sper- 

 mathecae; allow rest to mate a second time, pairing some with their 

 former mates and others with different mates : kill all and examine sper- 

 mathecae." 



In plants and animals where both sperm and eggs are found in the 

 same individual there is usually a different period for the maturing of 

 each or some apparatus like this of the earthworm is brought into play 

 so that it is very seldom that the same organism can fertilize itself. 



The sperm-mother cells are derived from the testes and deposited in 

 the seminal vesicles. They are not fully developed, or as we say, "ma- 

 ture," however, when they leave the testes, and so must continue their 

 development in the seminal vesicles. 



The sperm-mother cells or primordial germ-cells from which the 

 sperm are developed in the testes, have their nuclei divide into 2, 4, 8, 

 or 16 daughter nuclei which become arranged in a single layer near the 

 periphery of the protoplasm which has not divided. Cell walls then ap- 

 pear extending inward into the undivided protoplasmic mass. These 

 newly-formed cells now divide again, forming as high as from 32 to 128 

 cells when the whole mass breaks up into smaller colonies. These 

 nucleated cells which are to become sperm are called spermatogonia. 

 These spermatogonial colonies become spherical, each containing 32 pri- 

 mary spermatocytes, all of which are still fastened by cytoplasmic 

 threads to the central protoplasm. This whole 32 celled colony is now 

 called a blastophore. 



Each colony of primary spermatocytes "gives rise to 64 secondary 

 spermatocytes, and these divide into .128 spermatids. The latter then 

 metamorphose ( ) into spermatozoa, The number 



of chromosomes in the spermatozoa is sixteen ; this is one-half the num- 

 ber contained in the somatic cells, the reduction having taken place dur- 

 ing maturation by the union of the chromosomes two by two in the sec- 

 ondary spermatocytes, and a subsequent separation when the spermatids. 

 were formed." 



The head of the spermatozoon is practically all nuclear material, 

 the mid-piece is what was formerly the centrosome, while the cytoplasm 

 formed the tail. But as it is only the head which actually enters and 

 fertilizes the egg, the tail being used only for locomotive purposes, it 

 will be seen why nuclear material is considered so very important. 



