150 THE VARIATION OF ANIMALS IN NATURE 



Drosophila has a significant effect in reducing the time taken 

 by the male to succeed in copulation. Males with their wings 

 removed are able to mate sooner or later, but in them the 

 pre-mating period is longer. In the Lepidoptera the experi- 

 ments of Fabre, Mayer and Freiling have shown that the scent- 

 apparatus of the female is frequently (probably nearly always) 

 an essential element in pairing. The males are normally 

 attracted to the scent of their own female, who distributes it 

 until pairing has been effected. In some fireflies, different 

 species of a genus emit light of different colours or in flashes of 

 different frequency. Where both sexes are luminescent, each 

 sex may respond only to the signal of its mate (Coblentz, 

 191 1 ; Macdermott, 1910, 191 1, 19120, 1912^). In the 

 Mollusca, Diver (quoted by Robson, 1928, p. 126) has shown 

 that the two common English banded snails (Cepea hortensis 

 and C. nemoralis) differ in the energy with which mating 

 individuals stimulate one another with their darts. This 

 difference, which appears to have no connection with the 

 actual structure of the dart (which is also specific), is normally 

 sufficient to keep the species apart if they attempted to 

 pair. 



Standfuss (1896) was able to show that the females of the 

 Italian subspecies persona of Callimorpha dominula (Lepidoptera) 

 are scarcely attractive to the males of the normal form. 

 Grosvenor also (1921) has found local variations in the 

 attractiveness of the female in ^ygaena (Lepidoptera). 



In the Orthoptera, where sound-production plays an 

 important part in courtship, Fulton (1925) has shown that 

 two biological races of the tree-cricket, Oecanthus niveus, differ 

 in their song. Faber (1928), however, in his study of the 

 German Orthoptera, found that by no means all species could 

 be separated by their song, which, further, was very variable 

 owing to the influence of temperature and the rivalry of other 

 males. Whether a species responds only to the song of its 

 own kind appears still to require much more confirmation. 



In spiders, Bristowe and Locket (1926) show that courtship 

 antics and male decorations may have a real value as recog- 

 nition marks. It appears that unless the female recognises the 

 male as belonging to her species she will often eat him, and the 

 peculiar dances of the males assist the females to avoid mistakes. 

 Tactile stimuli may play a similar part in families where sight 



