"THE RISE OF LAND LIFE 33 



release and escape from old limitations into a host of new 

 possibilities. Says Lull: ''The sea is so changeless and the 

 range of its conditions so small that evolution within it is 

 not stimulated as it is on land." ^ Life is far more complex. 

 The animal is continually pelted with new stimuli and expe- 

 riences; hence the large size and accompanying long life of 

 the individual, the storing up of the results of these experi- 

 ments in the growing, changing impressible brain. Not yet, 

 but some day, the land-vertebrate will become intelligent. 



But life on land and in the air initiated changes of greater 

 importance though of far slower realization than any which 

 we have yet noticed. The development of the muscular and 

 nervous systems is accompanied by a more rapid combustion 

 of food material; they are expensive luxuries. Hence, as we 

 have seen, the surplus devoted to reproduction, enormous in 

 parasites, very large in sessile or slow moving forms, is fast 

 sinking to a minimum. Yet speed and muscular and nervous 

 energy will increase still more rapidly from this time on. 



This rapid decrease of surplus for reproduction is a danger 

 signal; it suggests or threatens race suicide. We remember 

 that the number of eggs must be inversely proportional to their 

 size; and the size of the egg is determined chiefly by the 

 amount of nutriment required to support the embryo until 

 it can shift for itself. This again is determined by the 

 complexity of the animal and the conditions accompanying its 

 birth. If a form is born in water, like a fish or tadpole, it 

 can almost float to its food. It swims by vibrations of the 

 tail, and thus requires only the action of masses of simple 

 trunk muscles stimulated and controlled by a very simple 

 nerve-center. The animal born on land must walk to its food. 

 This demands a considerable development of complex sets 

 of muscles controlled by a correspondingly complex brain. 

 This again demands a steadily lengthening period during 

 which the embryo must be supported, boarded as it were. 



In one word every egg of an animal born on land must be 

 far larger than of one born in the water. The young of am- 



2 H : 479- 



