302 DARWINISM AND THE PROBLEMS OF LIFE 



germ-cells ? In this case, naturally, the germ-cells 

 alone enter into amphimixis. The division of labour 

 has advanced so far in the volvox that the germ-cells 

 which reproduce the animal in the non-sexual way 

 we have described cannot enter into amphimixis. A 

 different kind of germ-cells has been provided for this ; 

 these also are found in the cell cluster of the volvox, but 

 they are only formed from time to time. In fact, there 

 has been a division of labour even amongst these sexual 

 germ-cells. There are two kinds of them produced in 

 the same animal, so that at the proper moment a volvox 

 has four sorts of cells — body-cells, asexual germ-cells, 

 and two kinds of sexual germ-cells. 



One of the latter kinds is comparatively large, and is 

 only formed in small numbers ; and they resemble the 

 asexual germ-cells. The cells of the other kind lie in 

 packets, each containing several, in the volvox body. 

 These cells are very small and have mobile lashes, like 

 the body-cells. They break away, when they are 

 mature, and seek another volvox, and combine with its 

 sexual germ-cells of the first kind. The product of the 

 fusion then dissolves, and develops into a new animal. 



In the volvox we have the same features that we find, 

 essentially, in all the higher animals. In these, how- 

 ever, the asexual germ-cells have generally disappeared ; 

 they are common only in the plants, in the shape of 

 spores. With the disappearance of the asexual germ- 

 cells the animal is now reduced to one method of 

 reproduction, that following upon amphimixis. Never- 

 theless, the cases of parthenogenesis show that natural 

 selection can impart even to the sexual germ-cell, the 



