350 THE ZOOLOGIST. 



and that they are of sufficient frequency and magnitude, and that a 

 sufficient proportion of them lead in such directions that natural 

 selection can take advantage of them. Difficulties and objections 

 were raised, but morphology on the whole took little heed of them. 

 Remaining steadfast in its adherence to the principles laid down by 

 Darwin, it contented itself with piling up circumstantial evidence, 

 and met objection and criticism with an ingenious apologetic. In 

 brief, its labours have consisted in bringing fresh instances, 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 certain stage of scientific progress, 

 it does not help us to form new rules, and fails altogether if the old 

 rules are seriously called into question. 



As a matter of fact, admitting that the old rules are valid, it has 

 become increasingly 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, indeed, they could be said to occupy themselves 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 internal and 

 hidden laws. This defect seems to have been more distinctly realised 

 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 organism 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 follow 

 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 

 discussion of the significance of the patterns of the molar teeth of 

 mammals or a disputation about the origin of the ccelomic cavities 

 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 substantial 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 direction 

 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 concept of what may be expected to underlie form 

 and structure. Dealing, as they have dealt, almost exclusively with 

 things that can be seen or rendered visible by the microscope, they 

 have acquired the habit of thinking of the organism as made up of 

 organs, the organs of tissues, the tissues of cells, and the cells as 



