38 



THE YOUNG NATURALIST. 



marked difference in their size and colour. 

 Many double-brooded species present no 

 difference between those appearing in spring 

 or summer, while others are so distinct as 

 to have been thought different species. Mr. 

 Jenner Weir's remarks on Pieris napi, which 

 he selects as an illustration of Horeomorp- 

 hism, are most interesting. Those emerg- 

 ing in spring have a much larger proportion 

 of greenish grey scales on the upper side 

 than those appearing on the wing in July or 

 August. Dr. Weisman has discovered that 

 if the appearance of the summer brood be 

 retarded by placing the pupa in an ice safe, 

 it produces the spring form. He therefore 

 conjectures with some appearance of truth, 

 that the Alpine form of this insect known 

 as bryonia was the ancestral type. This 

 insect is much more densely scaled with 

 greenish grey than even our spring form, and 

 Dr. Weisman supposes it to have existed 

 here during the glacial period. As the tem- 

 perature became milder it became double- 

 brooded and paler, especially in the second 

 brood ; and when he forced it back to its 

 single-brooded condition the pale summer 

 form disappeared altogether. This is a 

 most interesting discovery, and Selenia illus- 

 traria is an exact parallel, the type, appear- 

 ing in spring, and having passed the winter 

 n pupa, being darker and more marked 

 than the summer brood known as /Estiva, 

 which is both smaller and paler. But we 

 must not generalize on insufficient material, 

 and Vanessa levana, a common continental 

 butterfly, which presents very marked 

 differences between the two broods, is very 

 much darker in the summer than in the 

 spring brood. Our own Vanessa C-album 

 passes the winter in the perfect state and 

 produces a paler form in early summer, to 

 be followed by the darker insect that 

 emerges in autumn and hybernates. An- 

 other regularly-occurring form of variation 

 is that where the sexes are not alike. The 

 structural difference between the antennas 



of the sexes is due to other causes than 

 those that have produced the change in the 

 hue or marking of the wings, and it is with 

 the latter only I have to do at present. 

 These are most distinct in butterflies and 

 bombyces, and some very interesting illus- 

 trations may be found among British 

 species, though there are some still more 

 extraordinary cases to be found among 

 Exotic Lepidoptera. 



This paper is already longer than it 

 ought to be, and the branch of the subject 

 now under consideration is scarcely touched 

 upon. I must leave it for the present, but 

 will return to it again when opportunity 

 affords. 



BOTANICAL 

 NOMENCLATURE. 



(From the "Pharmaceutical Journal and 

 Transactions). 



Although, under the influence of the 

 new school of physiologists, botany is rapidly 

 losing its reproach of being a mere science 

 of classification, its system of nomenclature 

 is perhaps the most perfect of any of the 

 natural sciences. This is mainly due to 

 the fact that several of the most illustrious 

 botanists of recent times, — among whom 

 must especially be mentioned two still 

 living, Alph. De Candolle, of Geneva, and 

 our own veteran, Mr. Bentham, — have ap- 

 plied their great powers especially to the 

 perfecting of the laws of nomenclature. 

 The system now all but universally adopted 

 was formulgated in a canon of sixty-eight 

 articles laid down by a Congress held for 

 the purpose at Geneva in 1867, which origi- 

 nated mainly with M. De Candolle. The 

 experience of the sixteen years which have 

 elapsed since then has suggested some slight 

 modifications or extensions of these articles, 

 which are published in a brochure by the 



