154 SUMMARY AND CONCLUSION. 



lution. In order to perfect the method it is important that the crea- 

 tures under study should be labeled at the time of collection with the 

 conditions (of feeding, etc.) under which each specimen was found, 

 and should be exhibited on maps setting forth as fully as possible the 

 conditions presented by the environment at each point. An impor- 

 tant step in this direction has been made by the late Professor Hyatt, 

 of the Museum of the Boston Society of Natural History, in construct- 

 ing a model of the island of Oahu, on which the geographical relations 

 of the species and varieties of snails from that district may be exhib- 

 ited. It would, however, be a great gain if a model (or at least a map) 

 of the island of sufficient size were so arranged as to allow the shells 

 themselves to be placed upon it in their true positions, instead of 

 being represented by letters and numbers. The advantage of both 

 methods might be attained by having, in addition to the model of 

 the island arranged according to Professor Hj^att's method, a very 

 large map on which the shells might be placed. 



The method might be further improved by the use of colors and 

 other devices for indicating the species of plant on which each speci- 

 men was found. The influence of temperature, humidity, and other 

 external conditions, and especially of the conditions interfering with 

 free crossing, may also be studied by exhibiting the average character 

 attained under different stages of the influence and the degree of seg- 

 regation resulting from the full action of the combined influences. 



The degrees of segregation that have taken place in the inhabitants 

 of a series of districts presenting different degrees of geographical 

 isolation may also be studied by the determination of place-modes by 

 statistical methods. Information on the mathematical methods that 

 have been applied to this and other allied problems in biology will be 

 found in the works of Francis Gal ton, Karl Pearson, C. B. Davenport, 

 and others, and in "Biometrika/' a journal for the statistical study 

 of biological problems. 



3. The Study of Conditions Favoring Segregation. 



A rich field for the study of organisms under conditions favoring 

 segregation will be found in the fauna and flora of island groups. The 

 most interesting conditions will appear where the majority of the 

 species are able to distribute themselves with some degree of freedom 

 from island to island, while some one organic form is unable to pass 

 the water barriers, except on very rare occasions. In such a region 

 we shall, I believe, always find a series of nearly related varieties or species 

 distributed in the midst of a comparatively uniform environment. Simi- 

 lar results will undoubtedly be found wherever a group of organisms 



