Experiments with Snails, Moths, and Beetles 141 



Individuals of these two species also show other antagonistic 

 characters. There are size differences, and these also Mendelize. 

 The form of the navel also differs and gives a fourth character. 



The preceding breeding experiments relate to differences 

 within the species, but Lang has also carried out experiments 

 between the two species, H. hortensis and H. nemoralis. The 

 results will be described in the next chapter. One point of 

 interest must, however, be mentioned here. As stated above, each 

 species contains individuals that are banded or bandless, red 

 or yellow, etc. These are varietal differences. The point of 

 interest is that when the two species are crossed the offspring — 

 species hybrids — show that one of the antagonistic characters 

 dominates in the same way as when the varieties within the spe- 

 cies are crossed. For example, if a bandless individual of Helix 

 hortensis is paired with a five-banded individual of Helix nemo- 

 rahs, the hybrids are in some cases entirely bandless, in other 

 cases partly bandless and partly five-banded. Lang accounts for 

 these results by assuming in the first case that a '' pure " bandless 

 form was used, all of whose germ-cells were " pure " and hence 

 dominated; while in the other case a dominant recessive was used 

 which would produce both kinds of germ-cells. On the other hand, 

 one should not lose sight of the fact that the hybrid-crossing may 

 itself set "free" latent characters, as in mice, so that the results 

 may have arisen in this way. Lang concludes that those varietal 

 characters that Mendehze within the species behave in the same 

 way w^hen different species are crossed. 



Experiments with Silkivorms 



Elaborate series of experiments with silkworms have been 

 carried out by Coutagne.^ The results of ten years' work were 

 pubhshed in 1903. Although ample evidence is furnished of 

 alternative inheritance, the results are not treated by the author 

 from the point of view of Mendel's law, although there are indica- 

 tions in many places that some at least of the results might profit- 



^ Bulletin Scientifique de la France et de la Belgique, XXXVII, 1903. 



