326 



The Journal of Heredity 



while the Mcndelian heredity which is 

 determined by the nucleus adds only 

 the finer details to the rough block. 

 Such a possibility exists, and if it 

 should turn out to be true we should 

 come to the conclusion that the unity 

 of the organism is not due to the putting 

 together of a number of independent 

 Mendelian characters according to a 

 'pre-established j^lan,' but to the fact 

 that the organism in the rough existed 

 already in the cytoplasm of the egg 

 before the egg was fertilized. The 

 influence of the hereditary Mendelian 

 factors or genes consisted only in 

 impressing the numerous details upon 

 the rough block and in thus determining 

 its variety and individuality."^ 



Primitive biology supposed that the 

 egg consisted of homogeneous material 

 which had to be differentiated into an 

 organism. For this supernatural task 

 sujjernatural agencies seemed to be 

 required, and it is not surprising that 

 many biologists imagined some quasi- 

 sui^erhuman intelligence which presided 

 over the development of life. But when 

 it is found that the tmfertilized egg 

 contains the rough structure, who.se 

 creation is due to the fact that the 

 egg is laid down a little at a time in the 

 ovary, Dr. Loeb thinks there should 

 be no difficulty about discarding the 

 superstitious view and seeing merely 

 mechanical processes. 



5. If a piece of twig is cut froin a 

 willow or rose, and stuck in the ground, 

 leaves will grow from the up])er end 

 and roots from the lower; so that the 

 part regenerates the whole original 

 plant. Similar effects can be produced 

 in lower animals, and even in higher 

 £inimals a purl which is cut off may grow 

 again. Is there an\'thing mysterious 

 about this power ? Must it be supjxjsed, 

 with (i. Wolf, that the organism has a 

 knowledge of its own needs; or that 

 there is some intelligent guidance of it, 

 either inside or outside of it? On the 

 contrary, Dr. Loeb says, "it can be 

 shown that the organism does in this 

 case what it is comi)elled to do by its 

 physical and chemical structure." 

 There is no miracle to be found here, 



unless one also finds a miracle in the 

 fact that water runs down hill. To 

 state the case as simply as possible, 

 it may be said that there are certain 

 organ-producing substances constantly 

 in circulation in a plant or animal. 

 As long as these circulate, they do not 

 produce organs; but if their circulation 

 is stopped, they start growth at the 

 point where they collect. Thus in 

 the geranium-cutting which is jjlanted 

 in sand by the gardener, there are 

 root-producing substances and leaf- 

 producing substances in circulation. 

 The leaf-producing substances flow to- 

 ward the apex, are stopjjed there, and 

 gi\'e rise to the production of leaf -buds. 

 The root-producing substances, which 

 are being carried toward the base, 

 collect at the base and start the forma- 

 tion of roots. The existence of these 

 specific organ forming substances is 

 now well demonstrated; they are now 

 known as "internal secretions" or 

 "hormones." 



THE PROBLEM OF INSTINCTS 



6. So far, it may be said, the mechan- 

 ist has had relatively easy problems. 

 The problem of development itself 

 might even offer no embarrassment ; but 

 how can he explain the complicated 

 instincts which make for species preser- 

 \'ation and j^erpetuation ? 



"The idea that the organism as a 

 whole cannot be explained from a 

 physicochemical viewpoint rests most 

 strongly on the existence of animal 

 instincts and will. Alany of the instinc- 

 tive actions are 'jjurposeful,' i. e., 

 assisting to preserve the individual and 

 the race. This again suggests 'design' 

 and a designing 'force,' which we 

 do not find in the realm of physics. 

 We must remember, however, that 

 there was a time when the same 'pur- 

 l)osefulness' was believed to exist in 

 the cosmos where everything seemed to 

 turn literally and metaphorically around 

 the earth, the abode of man. In the 

 latter case, the anthropo- or geocentric 

 view came to an end when it was 

 .shown that the motions of the planets 

 were regulated by Newton's law and 



'This view has been woll criticifed by L. C. Dunn: Nucleus and cytoplasm as vehicles of 

 heredity. American Naturalist vol. li, pp. 286-301, May, 1917. 



