﻿352 J. DEWITZ — THE BEARING OF PHYSIOLOGY 



As previously mentioned, adult caterpillars of Porthesia chrysorrhoea, while in 

 process of transformation, were put into an atmosphere containing hydrocyanic 

 acid gas and resulted only in pupae with very small wings, devoid of chitin, 

 and of colourless body, all indications which are likewise present as a result of 

 want of oxygen. 



"Contact" liquid insecticides have in a similar way been accepted and 

 generally used without any questions being asked as to the nature and basis of 

 their efficiency. It was generally asserted and assumed that the " contact " 

 liquid penetrates into the tracheae, thereby suffocating the insect. Microscopical 

 examination reveals the fact that liquid does penetrate into the tracheae ; but 

 such penetration is in most cases so very incomplete that it cannot possibly be 

 accepted as causing the insect to perish by suffocation. Moreover there are 

 numerous ii contact " insecticides in the form of powder, and surely no one can 

 believe that their efficacy consists in filling the tracheae and choking the insect. 

 The stigmata of insects are far too small to permit of this and they are 

 frequently protected in a special manner. I am rather inclined to believe that 

 contact insecticides, both liquid and as powder, have a fatal effect upon the sense 

 organs of insects. 13 Fujitani's 19 statement that the active agent of Pyrethrum is 

 a nerve and muscle poison, to which fishes and insects are very sensitive, will 

 go far to confirm my view. 



It is somewhat early to speak of the influence of sucking insects on plant 

 organs in the sense of the effect of enzymes of fungi on them, although a 

 few observations thereon are known. But in view of our present knowledge 

 of enzymes and toxins it would be futile to deny a direct chemical action of 

 all sucking insects upon plant organs. Why should not the puncture of an 

 Aphis or of a Phylloxera, which thereby transforms the organ of the plant, 

 transfer toxic substances into the plant tissues in the same way that the sting of 

 a scorpion or of a bee introduces toxins into the organism of man or other 

 animals ? 



If the above comments and tentative intimations on only a few entomological 

 and physiological subjects of general interest, which are familiar to me, 

 contribute to bring home only a part of the important bearing of physiological 

 research upon Applied Entomology, we shall come nearer to the time when 

 physiology will occupy that eminent place in connection with insect pest research 

 which, by its very nature and intrinsic value, it should hold. 



Bibliography. 

 Bataillon, E. 



1. La metamorphose du ver a soie et le deter minisme cvolutif ; Bull. Scient. 



France et Belgique, xxv, p. 18-55 (1893). 



2. Les metamorphoses et Fontogenie des formes animales ; Rev. Courguign. 



d. l'enseignement superieur, 1893, pp. 1-32. 



3. Nouvelles recherches sur les mecanismes de revolution chez le Bombyx 



mori; op. cit. xiv, no. 3, pp. 1-16. 

 Dewitz, J. 



4. Ueber die Vereinigung der Spermatozoen mit dem Ei ; Arch, gesamt. 



Physiol, xxxvii, p. 219-223(1885), xxxviii, p. 358-386, 1 taf. (1886). 



