290 THE CELL 



into a bundle of from sixteen to thirty-two spermatozoids (Fig. 158 

 M l ). They are "extended bodies, bearing anteriorly two cilia, the 

 original green colour of which has been transformed into yellow." 

 The individual bundles separate from the mother-colony, and swim 

 about in the water. "If they meet a female colony, the cilia on 

 both sides become entangled ; by this means the male colony is 

 fixed ; it however soon falls to pieces, after which the individual 

 spermatozoids, which become considerably longer, bore their 

 way into the gelatinous vesicle of the female colony. They then 

 make their way to the egg-cells, to which, after they have crept 

 round them, they attach themselves, often in great numbers. We 

 may assume that, as has been observed in many other cases, one 

 of these spermatozoids makes its way into each egg-cell " (Sachs). 



PIG. 159. Volvox glolator, sexual, hermaphrodite colony, somewhat diagrammatic repre- 

 sentation constructed from figures by Cienkovsky and Butschli (after Lang, Fig. 21 ) : s 

 male amete sermat 



novsy an 

 male gamete (spermatozoid) ; female gametes (eggs). 



Finally, in Volvox globator (Fig. 159) the differentiation is 

 greater than ever, for amongst the very numerous cells which 

 constitute the globular colony some remain vegetative, whilst 

 others become transformed into sexual cells. Further the eggs 

 (0) are still larger than in Eudorina, and are fertilised by very 

 small male elements (s), which swim about with two flagella. 



If we take all these numerous facts into account, we may surely 

 consider the following law as established, i.e. that egg and sperm- 

 cells are derived from reproductive cells, which, to start with, are 

 similar and not to be distinguished from one another, but which 

 become differentiated by developing in opposite directions. 



II. The Physiology of the Process of Fertilisation. 

 laving discussed the morphological phenomena which have been 



