412 NATURAL SCIENCE. June, 



not in its physical, but in a broad philosophical sense, and points out 

 that the new-fangled word " Mechanik," used in this way, has no 

 advantage over the old-fashioned term " Lehre." The latter covers 

 the same ground, and at least cannot mislead. Now Lotze, in 1842, 

 and Roux in 1880, both used the word " mechanics " to express widely- 

 differing ideas. Lotze used it in the stricter physical sense, in 

 opposition to certain writers whose vitalistic theories were supposed 

 to explain all otherwise inexplicable phenomena of life ; but Roux, 

 while drawing attention to the work of Lotze, uses his word with a 

 much wider and less definite meaning, in fact in several senses. 



With regard to the newness and importance of Roux's doctrine 

 of the causes of organisation. Professor Hertwig considers that his 

 opponent deceives himself on both points. Seeing that Lotze in 1851 

 wrote of the mechanical explanation of life as a task to which more 

 and more workers were then addressing themselves, it can hardly be 

 reckoned as one of the latest developments of modern science. Kant, 

 Wolff, and Schwann all had, in their turn, the same end in view. 

 According to Kant, every science is a mechanical one, but to tack on 

 the word " mechanics " to zoology and re-christen it " zoomechanics "^ 

 in a general philosophical sense is not to create a new science. It is, 

 however,with the methods of the "causal morphologists" that Professor 

 Hertwig is most inclined to quarrel. Roux claims that zoomechanical 

 methods are of primary importance, that those of the descriptive 

 zoologists only prepare the way for causal investigators, and are of 

 little or no intrinsic value : their very facts are scarcely worth 

 having. Perhaps, if descriptive zoologists confined themselves, as 

 Roux appears to think they do, to details of external anatomy, his 

 strictures might have greater truth, but Professor Hertwig does not 

 seem to consider Roux necessarily the best judge as to the value of facts 

 supplied by the methods the latter depreciates. " To me," says our 

 author, "nature is at least as trustworthy a teacher as the 

 experimental anatomist." The methods upon which Roux lays most 

 stress are those which he calls " analytical causal thought " and 

 "intellectual anatomy," instruments of investigation which Professor 

 Hertwig does not think will, unaided, be found very advantageous. 

 Embryology is the branch of biology which can least be studied by 

 analytical or mathematical methods, and the tendency of the " causal 

 morphologists " to bring mainly these processes to bear upon 

 biological — and especially embryological — problems, and to reject 

 direct and constant observation in favour of purely experimental 

 work, Professor Hertwig regards as mischievous. Experiment and 

 observation should, he considers, go hand-in-hand, and there would 

 be small chance of original discoveries of lasting value if experiment,, 

 instead of being a means to an end, came to be regarded as an end in 

 itself. Probably many who think that merely statistical experiments 

 are too often so regarded in these days will be inclined to agree with 

 him. The great zoological discoveries of the age have certainly been 



