lyo\T:MBEB 25, 1910] 



SCIENCE 



733 



concept of what may be expected to under- 

 lie form and structure. Dealing, as they 

 have dealt, almost exclusively mth 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 made up — of what? 

 Of vital units of a lower order, as several 

 very distinguished biologists would have us 

 believe; of physiological units, of micellEe, 

 of determinants and biophors, or of pan- 

 genes ; all of them essentially morphological 

 conceptions; the products of imagination 

 projected beyond the confines of the vis- 

 ible, yet always restrained by having only 

 one source of experience — namely, the 

 visible. One may give unstinted admira- 

 tion to the brilliancy, and even set a high 

 value on the usefulness, of these attempts 

 to give formal representations of the gene- 

 sis of organic structure, and yet recognize 

 that their chief utility has been to make 

 us realize more clearly the problems that 

 have yet to be solved. 



Stripped of all the verbiage that has 

 accumulated about them, the simple ques- 

 tions that lie immediately before us are : 

 What are the causes which produce 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 eflEect be- 

 tween 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 researches of 

 the experimental morphologists and embry- 

 ologists directed towards the very aim that 

 Hofmeister proposed. Originally founded 

 by Roux, the school of experimental em- 

 bryology has outgro\^Ti its infancy and has 

 developed into a ^agorous youth. It has 



produced some very remarkable results, 

 which cannot fail to exercise a lasting in- 

 fluence on the course of zoological studies. 

 We have learned from it a number of posi- 

 tive facts, from which we may draw very- 

 important conclusions, subversive of some 

 of the most cherished ideas of whilom 

 morphologists. It has been proved by ex- 

 periment that very small changes in the 

 chemical and physical environment may 

 and do produce specific form-changes in 

 developing organisms, and in such experi- 

 ments the consequence follows so regularly 

 on the antecedent that we can not doubt 

 that we have true relations of cause and 

 effect. It is not the least interesting out- 

 come of these experiments that, as Loeb 

 has remarked, it is as yet impossible to con- 

 nect in a rational way the effects produced 

 vdth the causes which produced them, and 

 it is also impossible to define in a simple 

 way the character of the change so pro- 

 duced. For example, there is no obvious 

 connection between the minute quantity 

 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 (nor- 

 mally .26 per cent, magnesium sulphate 

 and .1 per cent, calciiun 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 pro- 

 duced specific effects on the eyes of devel- 

 oping embryos of the minnow Fundulus 



