470 THE ZOOLOGIST. 



and the details of management he gives with regard to the 

 keeping of such different creatures as Rats and Ducks are just 

 what we should expect of him. His range of experimental work 

 is wide ; either alone or with the help of friends he has bred and 

 studied not only the above-mentioned animals, but Dogs, Cats, 

 Pigeons, and African Desert-Mice (Meriones). Details of these 

 experiments are very full, and his book becomes one of those 

 indispensable for all students of heredity, for, although many of 

 the results have appeared in papers in scientific publications, it 

 is important to have them collected ; and the author's discussion 

 of rival theories is full and fair. The illustrations are full and 

 good ; three of them, representing some of the multiple hybrid 

 Ducks for which this experimenter is well known, being in colour, 

 while it may be mentioned incidentally that the book is of handy 

 size and well printed on a good paper. Mr. Bonhote's concep- 

 tion of vigour in animals is that it is comparable to " steam in 

 a boiler that must express itself in some form of energy, and 

 the higher the pressure the greater the energy. Nature has 

 several safety valves ; the chief and the one first used is out- 

 ward expression in colour, or in restless energy (song, emigration, 

 exercise, intellect, play, &c.) ; these, however, are minor outlets. 

 If, in spite of these, the vigour still rises, sexual intercourse 

 takes place, and the vigour of the resulting young is, if we may 

 so express it, analogous to the steam pressure in the second 

 cylinder." The characters of the young will depend on the 

 vigour of the parents at the time of mating, and many very 

 interesting instances of this are given in the experimental 

 details,, which also tend to discredit Mendelism as an universal 

 explanation of the facts of inheritance. The notion of sex- 

 developments as a safety-valve was enunciated rather fancifully 

 by J. G. Wood many years ago, and we are glad to find so up-to- 

 date an investigator as Mr. Bonhote scientifically confirms him. 

 "Where our author deals with non-experimental evidence, he 

 at times shows, like many zoologists even nowadays, a tendency to 

 make too-sweeping statements, as, for instance, where he credits 

 all Arctic animals, whose vigour he considers low, with a want of 

 very marked sexual differences, quite overlooking the very con- 

 spicuous ones found in the Narhwal, Harp-Seal, Bladdernose, 

 and the Long-tailed and Eider Ducks. 



