106 



gricollis, Mshm) may be quoted, as cases in point. Thus, 

 also, in Madeira, the Mycetoporus pronus, Erich., has a 

 large and small form, living in communion, which I 

 have never been able to connect, and yet which are un- 

 questionably identical (differing in no respect except in 

 size) : and so have the Stenus Heeri, Woll., and the 

 Saprinus nitidulus, Fab.* 



As regards the instability displayed by colour, in the 

 insect tribes, when subjected to the action of certain 

 conditions and influences from without, so much has 

 been said in the fourth section of the preceding chapter, 



* Although, in our ignorance of their real nature, we cannot cite 

 them as actually analogous to these separate phases in certain 

 members of the Insecta, yet we are forcibly reminded by the latter 

 of the distinct states which many of the Terrestrial Mollusca pre- 

 sent (frequently in equal proportions) in the same localities. Thus, 

 most of the Pupa have at least two abruptly-marked forms, a 

 larger and smaller one. Many of the Helices also exhibit this ten- 

 dency in an eminent degree : I have indeed been shown specimens 

 by Sir Charles Lyell of the Helix hirsuta, Say, from North America, 

 one state of which is considerably more than double the dimensions 

 of the other ; and I believe it is a well-known fact that intermediate 

 links have not yet been observed to connect the extremes. May 

 not therefore the gigantic H. Lowei and Bowdichiana, which are 

 now extinct in the Madeira Islands, have been but forms of the 

 H. Portosanctana and punctulata, respectively, co-existent with 

 them, though more sensitive to the great diminutions of altitude 

 and area which were consequent on the breaking-up of a once con- 

 tinuous land ? If such be the case, however, it is certain that they 

 were far commoner at an early period than their smaller colleagues 

 (which, now, in their proper districts, absolutely teem), seeing 

 that the latter are extremely rare in the fossil deposits, whilst they 

 themselves literally abound. 



