DEVELOPMENT. 145 



we see the same fact. An ordinary characteristic of inor- 

 ganic matter is its indefmiteness of form ; and this is also a 

 characteristic of the lower organisms, as compared with the 

 higher. Speaking generally, plants are less definite than 

 animals, both in shape and size — admit of greater modifica- 

 tions from variations of position and nutrition. Among ani- 

 mals, the simplest Ehizopods are not only structureless bat 

 amorphous : the form is never specific, and is constantly 

 changing. Of the organisms resulting from the aggregation 

 of such creatures, we see that while some, as the Foramini- 

 fera, assume a certain definiteness of form, in their shells at 

 least ; others, as the Sponges, are very irregular. The Zoo- 

 phytes and the Polyzoa are compound organisms, most of 

 which have a mode of growth not more determinate than that 

 of plants. But among the higher animals, w T e find not 

 only that the mature shape of each species is very definite, 

 but that the individuals of each species differ very little in 

 size. A parallel increase of contrast is seen in chemi- 



cal composition. With but few exceptions, and those only 

 partial ones, the lowest animal and vegetal forms are inhabit- 

 ants of the w 7 ater ; and water is almost their sole constituent. 

 Desiccated ProtopJiyta and Protozoa shrink into mere dust ; 

 and among the Acalephes, we find but a few grains of solid 

 matter to a pound of water. The higher aquatic plants, in 

 common with the higher aquatic animals, possessing as they 

 do increased tenacity of substance, also contain a greater pro- 

 portion of the organic elements ; and so are chemically more 

 unlike their medium. And when we pass to the superior 

 classes of organisms — land-plants and land- animals — we find 

 that, chemically considered, they have little in common either 

 with the earth on which they stand or the air which sur- 

 rounds them. In specific gravity too, w r e may note 

 the like truth. The very simplest forms, in common with 

 the spores and gemmules of higher ones, are as nearly as may 

 be of the same specific gravity as the water in which they 

 float ; and though it cannot b^ said that among aquatic 



