PARTULINA, SECTION BALDWINIA. 101 



tance. An adult shell once upon an isolated tree, one that is 

 separated from its fellows even by a few yards,, might live 

 and die leaving its progeny, if it chanced to 'be pregnant, to 

 perpetuate its peculiarities, subject only to the modifying 

 influences of such individuals ais by rare chance might be 

 blown to the same tree. 



Where shell-inhabited trees of the same species interlock 

 branches a more or less free interchange of inhabitants would 

 naturally take place, limited only by the natural sluggishness 

 of the mollusks, and, as a matter of observation, the forms of 

 P. confusa inhabiting closely adjacent pua trees were found 

 to be practically indistinguishable. 



' As bearing upon the problem of the variation of this 

 species, a most suggestive fact was noticed in connection with 

 the colonies upon the mamani trees. This is a small-leaved, 

 leguminous tree, and in appearance, and no doubt in fact, is 

 not well adapted to molluscan life. Yet generally where the 

 mamanis adjoined the pua trees, and invariably where they 

 touched branches, the mamanis were found to be occupied by 

 -colonies of confusa. These shells were almost always smaller 

 than those of the neighboring pua trees, often had diminutive 

 and distorted spires, and in every external aspect suggested 

 the effect of insufficient food or of unfavorable conditions r f 

 life. Whatever the explanation, the change of habitat from 

 -one species of tree to another closely adjoining has resulted 

 in establishing a recognizable form, striking evidence of the 

 plasticity of the Ackatinellidce, and of the slight nature of 

 what seem to be insurmountable barriers to free intercourse 

 between separate, but closely adjoining, molluscan colonies. 



" An examination of the embryonic shells of confusa dis- 

 closes that in a few of the more strongly marked forms the 

 embryo tends to perpetuate the color peculiarities of the 

 parent. Thus the young of the gray form are like their par- 

 ents, and are almost destitute of the zigzag markings which 

 decorate the spires of almost all the forms, but are often 

 wanting in adults of the gray variety. So, too, the young 

 of the brown shell, with brown and white body band, are 

 often but not always marked like their parents. But it would 



