102 ANIMAL INDIVIDUALITY [CH. 



Illustrating these theoretical points, there exist 

 for us, among various other examples, the members 

 of the family Volvocidae, an old but well-tried 

 object-lesson. These organisms, claimed by botanist 

 and zoologist alike, are members of the Flagellata, 

 unicellular organisms marked off by possessing long 

 whip-lashes or flagella with which they swim. The 

 Volvocidae seem to be a perfectly natural family. 

 They are all free-swimming ; they are all colonial, 

 with a framework of transparent jelly common to the 

 colony ; they all possess chlorophyll, nourishing them- 

 selves after the fashion of plants ; and they all have 

 two flagella, a single " eye-spot ' : and other morpho- 

 logical characters. There can thus be little doubt 

 that they are all descended from a single ancestor 

 who combined these common characters in his person. 



The different forms vary very much, however, in 

 the shape and size of the colonies, in the specializa- 

 tion of the sexual elements, and in the degree of 

 individuation of the colonies. 



At the base of the series stands Gonium sixteen 

 precisely similar flagellate cells embedded in firm 

 transparent jelly, joined in definite arrangement to 

 form a flat disc (Fig. 7). The colony thus constituted 

 lives and prospers, nourishes itself, and grows till comes 

 the time for reproduction. Then each cell of the 

 sixteen divides once, twice, thrice, and four times- 

 into sixteen little ones. Each of the sixteen groups 



