( lvi ) 
experiments, limiting my remarks almost exclusively to those 
relating to seasonally-dimorphic species. 
No doubt many of us remember with what interest we 
welcomed Weismann’s able treatise * published twenty-three 
years ago, whether in the original or in the English edition 
(translated by Prof. Meldola) issued in 1882. The cases 
known to Weismann, and described in this memoir, were not 
numerous ; he calls special attention to six European cases 
(Araschnia levana, Lycenu amyntas, L. agestis, Chrysophanus 
phleas, Pieris napi, and Euchloe belia), and to three North 
American (Phyciodes tharos, Grapta interrogationis and Papilio 
ajax), the latter known to science through the investigations 
of W. H. Edwards, the well-known monographer of the butter- 
flies of North America, whose experiments and results tT are 
re-published with additions as Appendix IT. to Weismann’s 
essay. In the phenomenon of seasonal dimorphism Weis- 
mann recognised, as two prominent factors in the possible 
direct influence of the varying external conditions of life, 
temperature and duration of the pupal period; and his ex- 
periments with Araschnia levana and Pieris napi were accord- 
ingly carried on with the view of ascertaining whether the 
dimorphism exhibited by those species could be traced to the 
direct action of those factors. In the case of A. levana, he 
first subjected the pupz obtained from eggs laid by the winter 
form, immediately after pupation, to artificial low tempera- 
tures, and the result was that, by exposure to temperature of 
0°—1° R. for four weeks, three-fourths of the pup produced, 
not the summer form prorsa—as under natural conditions 
they would have done—but the intermediate form porima 
(extremely rare in nature), three of these being very nearly 
the pure winter form devana. Increasing the period of ex- 
posure to cold to eight weeks did not materially add to the 
extent to which the summer form was lost and the winter 
form substituted. The converse experiment, frequently re- 
peated, consisted in placing in a hot-house (temperature 
* «Studien zur Descendenz-Theorie. I. Ueber den Saison-Dimorphis- 
mus der Schmetterlinge,” 1875. 
+ Canadian Entomologist, vii, p. 236 (1875), and ix, p. 69 (1879). 
