94 The American Geologist. ivinuary. i-.toi. 
might prove of material value in MoUusca, and through the 
aggregate effect of stability, power of resistance, and mechani- 
cal aptitude help any genius, enjoying these features, in the 
struggle of survival, and so lead to new and more advanced 
developments of the same elements, is quite possible, but it is 
clear that the fact of this development of size, skeletal mass, 
etc., throughout the organic impulse in the past, is more pro- 
foundly conditioned. 
In the first place the perpetuity of slight, small forms is 
quite as great as that of larger forms. The Lingula has out- 
lasted a wide range of heavier and more imposing brachiopods, 
and the unprotected cephalopods survive the marvellous 
"straight horns" and ammonites of ancient seas. The frail 
crinoids of our present ocean bottoms continue a line of de- 
scent quite contrasted with the well plated, high calyxed, teg- 
menated, and massive species of palaeozoic time. Gaster- 
opods and lamellibranchs have continuously enlarged up to 
present times, but the mere aspect of size, thickened shells and 
involved hinges seems in their case also utterly incomprehen- 
sible on the supposition of a survival. All the more so as along 
with the increase there continues a stream of small forms. It 
shows a distant biogenetic tendency. Even if natural selection 
finds in increase of size and molar complexity a field of ad- 
vantageous activity the continuous expression of these things 
reveals an implanted, not a succedaneous, motion in life, and,, 
partially at least, illustrates Prof. Osborn's dictum (Cart- 
wright Lectures, 1892.) "that evolution advances largely by 
the accumulation of definite variations, or those in which each 
successive generation exhibits the same tendencies to depart 
from the typical ancestral forms in certain parts of the body, 
and that these tendencies stand out in relief among the diffused 
kaleidoscopic or fortuitous anomalies." 
It remains for the conclusion of this first part of the pres- 
ent paper to demonstrate the fact of the growth in size and 
skeletal mass of the invertebrate forms of palaeozoic fossils. 
It is true that there is no consecutive line of symmetrical 
growth traceable upward with uninterrupted precision to a 
climax, with a subsequent regular decrescence. It is also true 
that along with growth in size and solidity and skeletal thick- 
enings and irregularities small primitive forms survive and 
