622 TRANSACTIONS OF SECTION D. 



changes in the forms of animals and plants? Are they purely internal, and, if so, 

 are their laws discoverable? Or are they partly or wholly external, and, if so. 

 how far can we find relations of cause and effect between ascertained chemical 

 and physical phenomena and the structural responses of living beings ? 



As an attempt to answer the last of these questions, we have the recent re- 

 searches of the experimental morphologists and embryologists directed towards 

 the very aim that Hofmeister proposed. Originally founded by Roux, the school 

 of experimental embryology has outgrown its infancy and has developed into a 

 vigorous youth. It has produced some very remarkable results, which cannot fail 

 to exercise a lasting influence on the course of zoological studies. We have learnt 

 from it a number of positive facts, from which we may draw very important con- 

 clusions, subversive of some of the most cherished ideas of whilom morphologists. 

 It has been proved by experiment that very small changes in the chemical and 

 physical environment may and do produce specific form-changes in developing 

 organisms, and in such experiments the consequence follows so regularly on the 

 antecedent that we cannot doubt that we have true relations of cause and effect. 

 It is not the least interesting outcome of these experiments that, as Loeb has 

 remarked, it is as vet impossible to connect in a rational way the effects produced 

 with the causes which produced them, and it is also impossible to define in a 

 simnle way the character of the change so produced. For example, there is no 

 obvious connection between the minute auantitv of sulphates present, in sea- 

 water and the number and position of the characteristic calcareous spicules in the 

 larva of a sea-urchin. Yet Herbst has shown that if the eggs of sea-urchins are 

 reared in sea-water deprived of the needful sulphates [normally CV26 per cent. 

 magnesium sulphate and "1 per cent, calcium sulphate), the number and relative 

 positions of these spicules are altered, and. in addition, changes are produced in 

 other organs, such as the gut and the ciliated bands. Again, there is no obvious 

 connection between the presence of a small excess of magnesium chloride in sea- 

 water and the development of the paired optic vesicles. Yet Stockard, by adding 

 magnesium chloride to sea- water in the proportion of 6 grams of the former to 

 100 c.c. of the latter, has produced specific effects on the eyes of developing 

 embryos of the minnow Fundulvs htttroditus : the optic vesicles, instead of being 

 formed as a widely separated pair, were caused to approach the median line, and 

 in about 50 per cent, of the embryos experimented upon the changes were so pro- 

 found as to give rise to cvclopean monsters. Many other instances might be cited 

 of definite effects of physical and chemical agencies on particular organs, and we 

 are now forced to admit that inherited tendencies may be completely overcome 

 by a minimal change in the environment. The nature of the organism, therefore, 

 is not all important, since it yields readily to influences which at one time we 

 should have thought inadequate to produce perceptible changes in it. 



It is open to anyone to argue that, interesting as experiments of this kind 

 may be. thev throw no light on the origin of permanent — that is to say. inherit- 

 able— modifications of structure. It has for a long time been a matter of common 

 knowledge that individual plants and animals react to their environment, but 

 the modifications induced by these reactions are somatic: the germ-plasm is not 

 affected, therefore the changes are not inherited, and no permanent effect is pro- 

 duced in the characters of the race or species. It is true that no evidence has 

 yet been produced to show that form-chnnges as profound as those, that T have 

 mentioned are transmitted to the offspring. So far the experimenters have not 

 been able to rear the modified organisms beyond the larval stages, and so there 

 are no offspring to show whether cvclopean eves or modified forms of spicules are 

 inherited or not. Indeed, if is possible that the balance of organisation of animals 

 thus modified has been upset to such an extent that they are incapable of growing 

 into adults and reproducing their kind. 



But evidence is beginning to accumulate which shows that external conditions 

 may produce changes in the germ-cells as well as in the soma, and that such 

 changes may be specific and of the same kind as similarly produced somatic 

 changes. Further, there is evidence that such germinal changes are inherited — 

 and. indeed, we should expect them' to be, because they are germinal. 



The evidence on this subject is as yet meagre, but it is of good quality and 

 comes from more than one source. 



There are the well-known experiments of Weismann. Standfuss. Merrifield. 

 and F. Fischer on the modification of the colour patterns on the wings of various 

 I.epidoptera. 



