36 BIOLOGICAL LECTURES. 



attained, the added power thus accumulated potentially in 

 large germs of double origin enabled the latter the more easily 

 to overcome untoward natural conditions. Natural selection 

 thus becomes altruistic or dotatjonaj in that it tends through 

 sexuality to defeat the deadliness of the struggle for existence, 

 just as we may also assert that the theory of superposition to 

 which the mechanical theory of development is committed is 

 also finally altruistic. It may be remarked that the greatest 

 mortality of a species, under the conditions of the struggle for 

 existence, also takes place in the egg and embryonic stages, or 

 before organisms can experience acute pain ; so that here 

 again we have a result that must materially ameliorate the 

 pains and penalties of the struggle for life. 



These details are, however, of minor import for us just now. 

 The important thing to bear in mind is that all of the forces of 

 development are ultimately metabolic in origin, and that the 

 wonderful order and sequence of events in any given ontogeny 

 arise from the transformation or transposition of the parts of a 

 molecular system, that also thus increases in bulk by the addi- 

 tion of new matter. The steps of this transformation are me- 

 chanically conditioned by dynamical laws with as much unerr- 

 ing certainty of sequence as those that control the motions of 

 the heavenly bodies. The consequence of such a view is that 

 we can thus free our minds of all traces of belief in a theory of 

 preformation. The embryo is not and cannot be preformed in 

 the germ, as observation and physiological tests prove ; nor is 

 such a preformation necessary if a mechanical hypothesis is 

 adopted. 



The egg cannot be isotropic as follows from observation as 

 well as experiment in the sense in which the word isotropy 

 is used by physicists of repute. If the egg is a dynamical sys- 

 tem it cannot be isotropic or absolutely the same throughout, 

 or along every possible radius from its center, as is proved by 

 its reactions in respect to its surroundings. It may, however, 

 be potentially aeolotrojpic in directions parallel to a certain axis, 

 as experiment has shown by separating the cells that result 

 from segmentation of the egg. Such fragments, if in excess 

 of a certain minimal size, will undergo a larval development of 



