.3,,. NOTES AND COMMENTS. 563 



transporting agency is that afforded by the feet and feathers of 

 wading and bathing birds ; for the commonest plants in isolated 

 ponds are the brittle species with finely-cut leaves, such as collapse 

 and cling when lifted out of the water. The associated molluscs 

 are usually the species that live among, or attach their eggs to, these 

 plants. 



With regard to the changes produced by environment, we may 

 also allude to some remarks by Mr. Robert Holland in the August 

 number of Nature Notes (vol. iii., pp. 147-152) which have reference 

 to similar observations previously published by Mr. Collingwood 

 Hope. It appears, as might be expected, that fishes placed in stag- 

 nant ponds soon become stunted, rarely growing to their normal size, 

 but it is interesting to have proved that even after several generations, 

 this dwarfing in the case of tench is not permanent, the small fishes 

 attaining their usual dimensions as soon as they are removed to a 

 shallow pond with a plentiful supply of fresh water. 



Economic Science. 

 Such observations, of course, have at present merely a philo- 

 sophical interest, and some of the lukewarmness in this line of 

 research may be due to the preference of many workers for subjects 

 that have an immediately economic bearing. In this connection it 

 is of interest to refer to the exhortation lately delivered by Professor 

 Herbert McLeod to one of the most economically-minded bodies in 

 the world of science — that of the chemists. In his recent Presidential 

 Address to the Chemical Section of the British Association, the Pro- 

 fessor refers to Faraday's well-known production of benzene from oil 

 gas in 1825, when this investigator had not the slightest idea that it 

 could ever have any practical application ; and he then quotes from 

 Professor A. W. von Hofmann's lecture on Mauve and Magenta in 

 1862, when the purely scientific discovery had become the basis of a 

 great industry. He quotes von Hofmann's peroration, and it will 

 bear reprinting again : — 



" Need I say any more ? The moral of Mauve and Magenta is 

 transparent enough ; I read it in your eyes. We understand each 

 other. W^henever in future one of your chemical friends, full of 

 enthusiasm, exhibits and explains to you his newly-discovered com- 

 pounds, you will not cool his noble ardour by asking him that most 

 terrible of all questions, ' What is its use ? Will your compound bleach 

 or dye ? Will it shave ? May it be used as a substitute for leather ? ' 

 Let him quietly go on with his work. The dye, the lather, the leather 

 will make their appearance in due time. Let him, I repeat, perform 

 his task. Let him indulge in the pursuit of truth — of truth pure and 

 simple — of truth not for the sake of Mauve, not for the sake of Magenta, 

 let him pursue truth for the sake of truth." 



" This," remarks Professor McLeod, " seems to be the true spirit of 

 the scientific investigator " ; and when as much is known of the funda- 

 mental principles of life as is already known about the Atomic and 



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