cxlviii GENERAL SUMMARY OF SCIENTIFIC AND 



plates. In the third section the transfonnation of the Mexican axo- 

 lotl into an Amblystoma is discussed at considerable length and 

 with characteristic thoroughness. Professor Weismann believes 

 that the Siredon or axolotl was originally derived from a land sala- 

 mander (AmUystorna), but has reverted to an axolotl or larval form 

 through the change of the climate of Mexico from a damp to an ex- 

 ceedingly dry one, obliging these animals, which as larvae lived in 

 ponds, and as adults formerly lived under trees and stones or in 

 damp places, to revert to the original larval siredon form and re- 

 main permanently amphibious. In the fourth division, " On the 

 Mechanical Conception of Nature," the author maintains that de- 

 velopment is mechanical, and that we must reject the idea of a spe- 

 cial life-force. Still he as strongly believes in teleology, and main- 

 tains the thesis that evolutional views do not lead to materialism. 



II. By Db. THEODORE GILL. 



One of the most important works of the year is a treatise, in two 

 volumes, " On the Geographical Distribution of Animals, with a 

 Study of the Relations of Living and Extinct Faunas, as elucidatino- 

 the 23ast Changes of the Earth's Surface," by Alfred Russell Wallace, 

 author of the " Malay Archipelago," and a co-discoverer with Dar- 

 win of the law of Natural Selection. This author has long been 

 favorably known as a geographical zoologist, and first defined the 

 boundaries between the Australian and Indian realms. 



He divides his subject into several parts. In the first part he dis- 

 cusses the principles and general phenomena of the distribution un- 

 der chapters, (1) introductory ; (2) the means of dispersal and the 

 migrations of animals; (3) distribution as affected by the conditions 

 and changes of the earth's surface ; (4) on zoological regions ; and 

 (5) classification as afi"ecting the study of geographical distribution. 

 In the second part he discourses on the distribution of extinct ani- 

 mals ; and in the third part he enters into a consideration of" zoolog- 

 ical geography : a review of the chief forms of life in the several 

 regions and sub -regions, with the indications they afford of geo- 

 graphical mutations." In a fourth and final part he considers the 

 geographical zoology in a systematic sketch under the different fam- 

 ilies of animals in their geographical relations. 



The older naturalists, says Mr. Wallace, " had a sort of vague no- 

 tion that certain forms were peculiar to hot climates, and that cer- 

 tain others w^ere only found in cold countries ; but that was about 

 all they knew or cared to know. Of the necessity of jDrecise knowl- 

 edge on the subject of locality they were absolutely incredulous. 

 To the modern naturalist, on the other hand, the native country, or 

 ' habitat,' as it is technically termed, of an animal or a group of ani- 

 mals is a matter of the first importance, and, as regards the general 

 history of life upon the globe, may be considered to be one of its es- 



