Movements of Insects. — BlachvaU. 51 



The foregoing solution of this interesting physiological problem I 

 have reason to believe is applicable not to insects ami spiders alone, 

 but also to some species of reptiles. 



Facts Relative to the Movements of Insects on Dry, Polished, Vertical 

 Surfaces. By John Blackwall, F.L.S. [From Journal of Lin- 

 iiaeau Society, vol. viii., p. 136.] 



As objections continue to be urged against the opinion that flies and 

 other insects of various species are enabled to move on the vertical 

 surfaces of highly polished bodies, by the emission of an adhesive 

 fluid from the numerous, hau'-like papillae distributed over the inferior 

 surface of their pulvilli, the statement of a feAv plain facts for the con- 

 sideration of dissentients, and especially of those who still advocate the 

 hypothesis, that flies, in such instances as those referred to above, are 

 supported in their movements mainly by the pressure of the atmos- 

 phere, may, perhaps, be deemed deserving of attention. 



Without the slightest intention to undervalue the importance of 

 microscopic researches into the organization of the parts in question, I 

 may be permitted to remark that the careful observation of phenomena 

 and judiciously selected and skillfully conducted experiments afford 

 equal if not superior advantages with regard to the determination of 

 the function they perform ; and that the two methods of investigatic n 

 should be pursued contemj)oraneously, and, as for as opportunities 

 will admit, in combination. 



Having clearly ascertained, by repeated inspections of the pulvilli of 

 flies under the microscope, both in a state of action and repose, that a 

 vacuum can not possibly be formed between them and smooth surfaces 

 to whicli they are applied, unless the papilla; with which they are pro- 

 vided separately contribute to produce such an effect, it was imme- 

 diately perceived that a decisive test of the truth or fallacy of this 

 conjecture might be obtained by means of the air-pumji, and the result 

 of its application was to demonstrate, not only that flies can traverse 

 the upright sides and the interior surface of the dome of an exhausted 

 receiver, while their physical energy is unimpaired, but also to estab- 

 lish the important fact that individuals occasionally remain fixed to 

 the sides of the glass after they have entirely lost the power of loco- 

 motion, a circumstance which admits of only one explanation, namely, 

 that an adhesive fluid is emitted from the extremity of their papilla^. 

 The' sole suggestion hitherto advanced, which has even the appearance 

 of at all affecting the validity of the conclusion thus arrived at, is, that 

 the specific gravity of flies is so low that a very slight degree of 



