NOTICES OF NEW BOOKS. 229 



The Penycuik Experiments. By J. C. Ewart, M.D., F.B.S., &c. 

 Adam & Charles Black. 



The title of this book may sound a little outr to some bio- 

 logists to-day, but cannot be misunderstood in the course of a 

 few years, when the breeding experiments of Prof. Ewart will be 

 more generally known to zoological science. Our readers will 

 remember a paper " On Zebra-Horse Hybrids," which appeared 

 in these pages last year, and which in the 'Penycuik Experi- 

 ments ' is reproduced. Penycuik is the Midlothian abode of 

 Prof. Ewart, who has now for some years followed the breeding 

 investigations that so long occupied Darwin ; and though to the 

 general public these are better known as the Zebra hybrid 

 experiments, much valuable work has been done with Pigeons, 

 Fowls, Dogs, and Babbits. The result, as might be expected, 

 leads to another nail in the coffin of our old fetish " species," and 

 the dogma as to its immutability. " Among plants, hybrids are 

 sometimes quite fertile ; while some crosses are quite, or almost, 

 sterile. There is no hard and fast line between species and 

 varieties, and hence there can be no fundamental difference 

 between a hybrid and a cross, nor yet any a priori reason why 

 any given hybrid should be sterile, or any given cross fertile. It 

 is no longer possible to contend that species were originally 

 endowed with mutual sterility, by way of preventing the con- 

 fusion that would result from free interbreeding." 



Prof. Ewart recognizes three distinct types of Zebras : — 

 Equus grevyi, E. zebra, and E. burchelli, which, ignoring the now 

 generally considered extinct E. quagga, is in agreement with the 

 views of Mr. Pocock (c/. Zool. 1897, p. 380). He has bred nine 

 Zebra hybrids by crossing mares of various sizes (from 11 to 15 

 hands) and breeds with his Zebra stallion, and possesses also 

 three hybrids out of Zebra mares, one sired by a donkey, the 

 other two by Ponies. The importance of these experiments is 

 clearly seen by the separate considerations and discussions on 

 such interesting biological problems or suggestions as — Bever- 

 sion, Prepotency and Inbreeding, Telegony, Saturation, and 

 Sterility ; while the conclusion is reached that " there is ob- 

 viously no real difference between cross-fertilization and inter- 

 crossing. Whether we interbreed or intercross, engage in ' line ' 



