194 



It is my opinion that classifications must be made, in the 

 first place, to deal only with the stvuctuves of animals at the 

 period of theh* greatest perfection in the individua]. The life- 

 histoi-y of the individual is a matter of extreme interest and 

 importanee; bat the attempt to combine the embr3^ological 

 dement with a Classification based on the highest development 

 attained by the species is a futile one, and can only increase 

 the difficulty of seeing even a little way into the excessively 

 complex Problems of modern biology. A systematic Classi- 

 fication is a very complex series of generalisations based on 

 the structure at which each species has ariived at the present 

 time: but embryology — of which branch of science the 

 knowledge of the metamorphoses of insects is eertainly a de- 

 partment — is on the other band an account of the roads by 

 which the structures classilied bave been reached. It thus 

 forms a department of knowledge of a kind quite distinct from 

 what I have attempted to deal with in the work kindly de- 

 scribed by Herr Bergroth. A comparative study of the results 

 arrived at by the two departments separately will be, after 

 each has been more perfeet, a matter of extreme inteiest. 



But I sball not pursue this (juestion farther, for 1 make 

 this explanation in order to make known the reason of my 

 silence about Schiödte's work on metamorphoses. 1 regret 

 however that I did not mention ifs existence in my introductory 

 remarks; for I would not have appeared to be wanting in 

 appreciation of this splendid production of the illustrious Pro- 

 fessor at Copenhagen. In a natural history, or biology, of the 

 üytiscidae Schiödte's work will occupy an important place, 

 but, as I have alread}' said, my memoir does not profess to 

 be a biology, and I have indeed expressly defined and limited 

 its scope in the following words at the commencement of the 

 memoir: „the memoir 1 otfer to the Society is a mere imperfect 

 sketch of the characters of the species of aquatic carnivorous 

 beetles, and a conti ibution to a synthetical or natural Classi- 

 fication thereof based on the external structures of the perfeet 

 insects.^^ 



Thornhill, Nov. 1882. 



D. Sharp. 



stell, entnmiil. Zeit. 1883. 



