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SCIENCE 



[N. S. Vol. XXKII. No. 830 



and reunited in different combinations in 

 the course of a few generations. "We do 

 not doubt the importance of the principle 

 of inheritance, but we are not quite so sure 

 as we were that close resemblances are due 

 to close kinship and remoter resemblances 

 to remoter kinship. 



The principle of variation asserts that like 

 does not beget exactly like, but something 

 more or less different. For a long time 

 morphologists did not inquire too closely 

 into the question how these differences 

 arose. They simply accepted it as a fact 

 that they occur, and that they are of suffi- 

 cient frequency and magnitude, and that a 

 sufficient proportion of them lead in such 

 directions that natural selection can take 

 advantage of them. Difficulties and ob- 

 jections were raised, but morphology on 

 the whole took little heed of them. Re- 

 maining steadfast in its adherence to the 

 principles laid down by Darwin, it eon- 

 tented itself with piling up circumstantial 

 evidence, and met objection and criticism 

 with an ingenious apologetic. In brief, its 

 labors have consisted in bringing fresh in- 

 stances, and especially such instances as 

 seemed unconformable, under the rules, 

 and in perfecting a system of classification 

 in illustration of the rules. It is obvious, 

 however, that, although this kind of study 

 is both useful and indispensable at a cer- 

 tain stage of scientific progress, it does not 

 help us to form new rules, and fails alto- 

 gether if the old rules are seriously called 

 into question. 



As a matter of fact, admitting that the 

 old rules are valid, it has become increas- 

 ingly evident that they are not sufficient. 

 Until a few years ago morphologists were 

 open to the reproach that, while they 

 studied form in all its variety and detail, 

 they occupied themselves too little — if, in- 

 deed, they could be said to occupy them- 

 selves at all — with the question of how 



form is produced, and how, when certain 

 forms are established, they are caused to 

 undergo change and give rise to fresh 

 forms. As Klebs has pointed out, the 

 forms of animals and plants were regarded 

 as the expression of their inscrutable inner 

 nature, and the stages passed through in 

 the development of the individual were 

 represented as the outcome of purely in- 

 ternal and hidden laws. This defect seems 

 to have been more distinctly realized by 

 botanical than by zoological morphologists, 

 for Hofmeister, as long ago as 1868, wrote 

 that the most pressing and immediate aim 

 of the investigator was to discover to what 

 extent external forces acting on the organ- 

 ism are of importance in determining its 

 form. 



If morphology was to be anything more 

 than a descriptive science, if it was to 

 progress any further in the discovery of 

 the relations of cause and effect, it was 

 clear that it must alter its methods and fol- 

 low the course indicated by Hofmeister. 

 And I submit that an inquiry into the 

 causes which produce alteration of form is 

 as much the province of, and is as fitly 

 called, morphology as, let us say, a discus- 

 sion of the significance of the patterns of 

 the molar teeth of mammals or a disputa- 

 tion about the origin of the ccElomic cav- 

 ities of vertebrated and invertebrated 

 animals. 



There remains, therefore, a large field 

 for morphology to explore. Exploration 

 has begun from several sides, and in some 

 quarters has made siibstantial progress. It 

 will be of interest to consider how much 

 progress has been made along certain lines 

 of research — we can not now follow all the 

 lines — and to forecast, if possible, the direc- 

 tion that this pioneer work will give to the 

 morphology of the future. 



I am not aware that morphologists have, 

 until quite recently, had any very clear 



