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SCIENCE. 



[N. S. Vol. VII. No. 162. 



of statistics. As by experiment we make 

 all causes similar except one and note the 

 result, so in statistics we select results hav- 

 ing at least one common cause and throw 

 all together, believing that, from the doc- 

 trine of chances, all other causes will offset 

 and annul each other. Thus we find, by 

 comparing the mean in the selected group 

 with the mean of the whole population, the 

 effect of the particular cause used as a basis 

 of selection. 



So much for definitions and general meth- 

 ods. But I have been asked to suggest 

 particular problems in morphogenesis and 

 the methods of their solution. Of ontoge- 

 netic problems we have the question in how 

 far is the development of the individual to 

 be explained as a series of responses to the 

 action of stimuli ; not merely of stimuli 

 external to the organism, but of part acting 

 on part ' as in the marvelous automaton' 

 — to use Aristotle's phrase. We get indi- 

 rect evidence upon this matter in studying 

 the capacity and laws of response in uni- 

 cellular organisms ; we get direct evidence 

 by applying particular agents, such as light, 

 heat and chemical substances, and noting 

 their effect on development. Again, we 

 have the question in how far the develop- 

 ment of the individual is determined by 

 wholly internal factors. To get an an- 

 swer to this question one must mutilate the 

 form and study the laws and limits of its 

 restoration — regeneration, reparation, heal- 

 ing, development despite untoward condi- 

 tions (as in dermoid cysts), and self- regula- 

 tion (or accommodation) in disturbed on- 

 togeny. In how far is the regeneration of 

 organism comparable with that of crys- 

 tals ? 



Next we come to a number of problems 

 connected with both ontogeny and phylog- 

 eny. Such are the problems of adaptation. 

 There is adaptiveness in those responses to 

 stimuli that are met with in development — 

 in tactisms, trophisms and differentiation. 



There is adaptiveness also in regeneration 

 and self-regulation of the organism. These 

 ontogenetic adaptations are often curiously 

 dependent on the past history and habits of 

 the species. Thus, Amoeba dwells in dim 

 light and is negatively phototactic, ems 

 of plants which live in the dark turn irom 

 the sun, parts of an animal most apt to be 

 lost are frequently those most capable of 

 regeneration. Is it due to selection or 

 is it an inherent quality of all protoplasms 

 that they should respond thus advanta- 

 geously ? Or is this whole phenomenon of 

 adaptation merely an ignis fatuus — this ap- 

 parent shaping of means to ends only a 

 necessary, mechanical relation? These 

 questions can be answered by paying atten- 

 tion to cases of unadaptive response and 

 unadaptive regeneration and regulation. 



Finally, the strictly phylogenetic prob- 

 lems deserve far more attention than has 

 yet been given them. Such are the ques- 

 tions concerning individual variation. It is 

 well known that in some cases the measure- 

 ments of an organ in the different indi- 

 viduals of a species group themselves about 

 a mean value in accordance with the nor- 

 mal probability-of error curve. In the case 

 of species undergoing change, however, the 

 curve is often very unsj'mmetrical or per- 

 haps has several maxima. What is the 

 precise meaning, in any case, of these ab- 

 normal curves? Again, how does the mode 

 (or the most common measurement) vary 

 with the habitat or geographical position of 

 the varieties of the species ? What is the 

 significance of those large variations which 

 we call sports and how do they differ in 

 origin from individual variations? What 

 sorts of variations in the body are corre- 

 lated? What is the morphogenetic kin- 

 ship of the various organs of the body? 

 Then there are the questions dealing with 

 inheritance : The laws of normal inherit- 

 ance—Do the progeny of a particular cross 

 inherit, on the average, equally from the 



