GENERATION OF ANLMALS, III. xi. 



and in one sense that they are spontaneously gener- 

 ated, in another that they are generated from them- 

 selves, or some by the one method, some by the 

 other. In \irtue of the Testacea being in their 

 nature the correlative of plants," no part, or only a 

 small part, of this tribe comes into being in the earth 

 (examples are snails, and any such species there may 

 be besides, but there are not many), whereas many 

 species, of all kinds of shapes, Uve in the sea and 

 similar watery places. The plant tribe, on the other 

 hand, makes very little show — practically none at all, 

 in fact — in the sea and such places, but all members 

 of this tribe grow in the earth. The reason is that 

 in respect of their nature the two tribes stand in 

 a correlative position ^ : the nature of Testacea is 

 removed from that of plants by an interval corre- 

 sponding to that by which water and fluid matter are 

 better able to support hfe than earth and sohd matter, 

 since Testacea aim at being so related to the water 

 as plants are related to the earth : it is as though 

 plants were a sort of land-shellfish, and shellfish a sort 

 of water-plant. 



And it is for some such cause as this that the things Various 

 which grow in the water are more various in shape pro^r\o 

 than those which grow in the earth. It is because various 

 a fluid substance is in its nature more plastic than 

 earth, and not much less substantial ; and this is a 

 characteristic possessed to a marked degree by the 

 creatures in the sea, since fresh water, though sweet 



stages are in order of increasing " perfection." We thus 

 get the avaXoyia (1. -21) : 



Testacea : Water : : Plants : Earth, or 

 Testacea : Plants : : Water : Earth. 

 * Or, " proportionate relationship." 



34-9 



