SCIENCE-GOSSIP. 



335 



believed sterility to have been. Speaking generally, 

 characters developed recently in the history of 

 species, are not reproduced in the bodies of 

 hybrids between them. For instance, none of the 

 zebra hybrids inherited the light ground colour of 

 the zebra (p. Ixvi.) sire. Again, the same thing 



Head of Bubchell's Zebra (Male). 



happens with cross breeding, which differs from 

 the other only in degree and not in kind. On the 

 other hand, animals which are inbred are found 

 to be prepotent, even in recently attained features, 

 and prepotency accompanies spots. 



In conclusion we might touch upon the question 

 of the ancestry and coloration of the horse tribe, 

 of which Professor Ewart speaks in several places. 

 Briefly, Hipparion of the Old and New worlds is 

 put down as the ancestor of the zebras and asses ; 

 while our modern horse is traced to Protohippus of 

 America (p. 113). 



The donkey type is considered to have early 

 separated from the zebras, whose coloration 

 (pi. xvi.) has become very specialized (except in the 

 extinct Equus quagga) by the darkening of stripes 

 and lightening of the ground colour. The stripes 

 (p. 123) still farther back arose from the coalescence 

 of spots, such as takes place dtxring the first year 

 or so in zebra-horse hybrids. A reversion to a 



spotted condition may also be seen in zebra-ass 

 hybrids. Professor Ewart distinctly separates 

 dappling in horses (p. 123), which is a variation 

 under domestication and may co-exist with stripes, 

 from the primaeval spots. 



It is distinctly stated that the stripes have no 

 relation to the ribs or to the course of nerves or 

 blood vessels in recent zebras ; but Professor Ewart 

 says they may have followed the latter in their 

 ancestors. This is not much svipport for Tyler's 

 theory, which seems to be rather a weak one. 



Of the types of coloration in zebras, much has 

 been discovered by the experimenter. No two 

 species or individuals are exactly striped alike ; 

 nor is one side of an animal identical in pattern 

 with the other. Three types are distinguished, 

 but not necessarily readily, as Professor Ewart 

 thought at first, by markings (p. x.) They are — 



Head of Hybrid, Zebra Male — Hoese Female. 



(1) Grevy's zebra {E. grevyi), of Shoa and 

 Somaliland : probably the one known at Rome in 

 the third century. 



(2) Mountain zebra (E. zebra), once abtmdant in 

 South Africa, and hence called the common zebra, 



(3) Burchell's zebra {E. hurchelU) ; this includes 

 several species or sub-species. 



There is no link missing in the chain of 



