RELATIONSHIP OF SPECIES. 451 



this animal is dead.) From what little I have been able to note 

 of hybridization and the bearing of habits in connection there- 

 with I should rather expect this cross to be sterile. (I have just 

 received information, which is I believe reliable, to this effect.) 



Beyond the fact that the Horse is apparently at one end of 

 the Equine line and the Ass and Zebra (Equus asinus and E. 

 zebra) at the other, nothing definite appears to be known about 

 the position of the remainder, viz., the various Quaggas and the 

 Asiatic species which might very well be more generally referred 

 to as Onagers. 



As regards that distinctive equine Grevy's Zebra (which com- 

 pares with the Mountain Zebra superficially, somewhat as a Poitou 

 Ass compares with our English donkey), some interesting blood 

 experiments have been made by Nuttall.* According to these 

 experiments, the blood relationship (in the majority of these 

 tests) appeared to be somewhat greater between Horse and Ass 

 than between Ass and Grevy's, and least between Grevy's and 

 Horse. Taking the very divergent results obtained by many of 

 these blood tests, it is perhaps unwise to attach too much 

 importance to them until thoroughly confirmed, but if correct, 

 the relationship of these forms might be written down as — 



Horse i i i a i Ass 



\, 



Grevy's 



Again, take the case of the two English Eats (Mus rattus and 

 M. decumanus), classed as species of one genus : these have few 

 special habits congeneric or common to both. 



I have been unable to breed any hybrid between these two 

 species, neither do I think they will copulate. Should they do 

 so and any produce result (which I should imagine unlikely, even 

 if they did copulate), it is probable the young would be sterile. 



As I am still experimenting with these animals, it is not at 

 present advisable to go further into the matter. 



* ' Blood Immunity and Blood Relationship.' 



