:352 JiANSAS CITY REVIEW OF SCIENCE. 



scribed actions which, on mature consideration, might be held to exhibit mental 

 processes of a certain kind. 



The speaker had lately put on record certain observations which seem to 

 indicate the possession by some species of the genus Helix, of the power to rec- 

 ognize a call or sound and distinguish it from other calls or sounds of a similar 

 character, and since then he has received several less exact communications seeming 

 to confirm this conclusion. It can hardly be doubted that in a group contain- 

 ing so many animals of a high degree of organization, such as the cuttles and 

 squids, for instance, mental processes of a tolerably complex nature must be car- 

 ried on in many cases. This subject has, as yet, received no attention. Anoth- 

 er important branch of the subject is the modification of organic life by physical 

 ■causes and the perpetuation of modifications by natural and sexual selection. 

 Mollusks occupy the middle ground between the higher groups of life, where 

 natural selection has its freest play, and those lower categories where its opera- 

 tions are veiled or inefficient. Investigation of the laws of variation among mol- 

 lusks is therefore especially desirable. 



The influences of natural selection are most evident, as they should be, in 

 ■those mollusks which, by their terrestrial habitat, are brought into the closest 

 •contact with enemies of relatively high intelligence, such as birds and other ver- 

 tebrata. The selected characteristics are chiefly of color. The grey and dull ap- 

 pearance of species inhabiting arid regions is well known. The speaker then de- 

 scribed many of the shells noticeable for their varieties and complexities of color, 

 • and the causes of these differences, as far as known. Among marine forms, the 

 struggle for existence, after the embryonic stages are past, is much less violent. 

 This arises partly from the much more uniform conditions of life in the sea, part- 

 ly from the general abundance of food contained in the sea water, and partly 

 'from the lesser intelligence of enemies which are chiefly fishes and predacious 

 -mollusks. Food has without question great importance, especially in determin- 

 ;ing certain tints of color. The speaker gave instances of the effect upon shells, 

 vin modifications upon them. Certain shells, said he, pick up and attach to their 

 upper surfaces bits of dead coral, stones and fragments of shell, until they 

 ^were entirely covered. Viewed from above, as they must be for the most part, 

 by fishes and carnivorous mollusks, nothing but dead and refuse material is 

 visible. It is evident that this system of clothing themselves by shells must be 

 a great protection, both from' enemies, which would pass them by, and from 

 accidental concussions. This must be confirmed as a habit by natural selection. 

 The character and disposition of the load has become so uniform in many cases, 

 as almost to take rank as specific characters. 



