1 882.] Transformations of Planorbn. 45 I 



physical influence of the immediate surroundings, varying with 

 every change of locality, but constant and uniform within each 



Third, that the Darwinian law of natural selection does not 

 explain these relations, but applies only to the first stages in the 

 establishment of the differences between forms or species in the 

 same locality. That its office is to fix these in the organization 

 and bring them within the reach of the laws of heredity. 



Fourth, that after this is done, they are inherited according to 

 the law of heredity with acceleration, which shows us in what 

 manner these differences and all other inheritable characters, 

 however originated, may with greater or less rapidity, become 

 incorporated in the young of descendant forms and species. 



Fifth, 1 that in these earlier stages they are more or less pro- 

 tected from change and may therefore remain comparatively inva- 

 riable through long periods of time, or may be exposed to great 

 changes in exceptional cases, and modified accordingly. 



Sixth, that these phenomena show, that fn growth, repro- 

 duction and heredity by acceleration, there is manifested a decided 

 reaction of the organism, which succeeds in building up and 

 maintaining the type structure and form, under all ordinary or 

 normal terrestrial conditions, but in some cases fails in fully ac- 

 complishing this when exposed to exceptional surroundings, as 

 in some cases of parasitism. 



Seventh, that gravity appears to be one of the causes of the 

 differences in effort, function and anatomy observed between the 

 sides or ends of animal forms when in vertical relations to each 

 other and to the earth, whether these be the anterior and posterior 

 ends of the form, or the dorsal and ventral, or the left and right 

 sides. 



Eighth, that the bilateral or geomalic growth observed in the 

 internal organs and the external parts of the organism when their 

 sides are in their original and hereditary positions, and the geo- 

 malic growth of the dorsal and ventral sides, when these become 

 horizontal through change of habit, appear to be directly or indi- 

 rectly, responses to the demands of gravity. 



Ninth, the origin of the limbs, etc., in pairs, while mere buds, 



