THE CELL AND PROTOPLASM. 107 



rid of still more of its chromatin material. Con- 

 sequently, the first division is followed by a sec- 

 ond (Fig. 39), in which there is again produced a 

 large and a small cell. This division, like the 

 first, occurs without any splitting of the chromo- 

 somes, one half of the remaining chromosomes 

 being ejected in this new cell, the second polar 

 cell (pc") leaving the larger cell, the egg, with 

 just one half the number of chromosomes normal 

 for the cells of the animal in question. Meantime 

 the first pole cell has also divided, so that we have 

 now, as shown in Fig. 40, four cells, three small 

 and one large, but each containing one half the 

 normal number of chromosomes. In the example 

 figured, four is the normal number for the cells 

 of the animal. The egg at the beginning of the 

 process contained eight, but has now been re- 

 duced to two. In the further history of the egg 

 the smaller cells, called polar cells, take no part, 

 since they soon disappear and have nothing to do 

 with the animal which is to result from the fur- 

 ther division of the egg. This process of the 

 formation of the polar cells is thus simply a device 

 for getting rid of some of the chromatin material 

 in the egg cell, so that it may unite with a second 

 cell without doubling the normal number of chro- 

 mosomes. 



Previously to this process the other sexual 

 cell, the spermatozoon, or male reproductive cell, 

 has been undergoing a somewhat similar process. 

 This is also a true cell (Fig. 34, me], although it 

 is of a decidedly smaller size than the egg and of 

 a very different shape. It contains cell sub- 

 stance, a nucleus with chromosomes, and a cen- 

 trosome, the number of chromosomes, as shown 

 later, being however only half that normal for 



