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VI. On the Comparative Influence of Periodicity and Tem- 

 perature upon the Development of Insects. By M. 

 C. Verloren, Med. Doc, Utrecht. Communicated 

 by Professor West wood, M.A., F.L.S., &c. 



[Read 6th August, I860.] 



Periodicity is an essential property of all organic being ; animals 

 and plants having, within fixed limits, a determined time of exist- 

 ence, growth and decay. In insects and plants this periodicity is 

 more expressed than in other classes of the organic creation ; in 

 the majority of species the different periods of development are 

 fixed to definite times of the year, diflTering, however, in different 

 species. 



It is generally known that temperature has great influence upon 

 periodicity. The experiments of Reaumur, in retarding or ad- 

 vancing the time of appearing of some insects, are sufficiently 

 known ; and Lacordaire has mentioned an observation, where 

 out of 100 pupae of Satiirnia Paphia, two-thirds came out after 

 fourteen days (the ordinary time of pupation), and the other one- 

 third at different times during ten subsequent months ; showing 

 that in that case the time of the year was without influence. 



But there are species in which the periodicity is only deter- 

 mined by the time of the year, and where temperature has no 

 influence thereupon. Swammerdam and Reaumur have already 

 made observations upon this subject. Swammerdam says, that 

 his Ephemera Swaviwerdamii always appears during three to four 

 days within the fourteen days between the feasts of St. Olof and 

 St. John ; and Reaumur states that another species of Ephemera, 

 inhabiting the Seine, always appears during two or three days be- 

 tween the 10th and 18th of August, adding that neither cold nor 

 rainy days had any influeuce thereupon. 



Besides this annual periodicity there is also a daily one. The 

 Ephemera of Swammerdam, according to his statement, appears 

 alvvays between the hour of 6 and 6.30 in the evening, and has 

 disappeared totally before 1 1 o'clock ; and Reaumur states of his 

 Ephemera, that it appears alvvays between the hour of 8 and 8.30 

 in the evening, and has disappeared at 10 o'clock. Brahm has 

 stated that Bomhyx Mori and Macroglossa CEtwtkerce leave the 

 pupa only at sunrise, Smerinthus Tilice at noon ; and Sciiroeter 

 states that sixteen specimens of Acherontia Atropos left the pupae 



