40 DR. J. MURIE ON IRREGULARITY [Jan. 13, 
ledge, are so stunted when full-grown. Thus it follows that either 
lessened dimension is a result of hybridity, or the two specimens a 
distinct species per se. 
In a conversation with my colleague Mr. Bartlett concerning this 
same question of hybridism and the size of the offspring, I received 
such information, based on his long experience among animals, that 
I think it worthy of incorporation in the present paper. From 
it some hints applicable to fish may be derived, or at least borne in 
mind, in discussing piscine forms. 
His proposition is, ‘That among all hybrids of vertebrated ani- 
mals there is a marked increase of size.’ In no instance coming 
under his observation has the offspring been smaller than both its 
parents. In other words, it is always larger than the lesser-sized 
parent ; that is, supposing inequality of dimensions between the 
parents to exist. 
Among Mammals the following examples may be cited :— 
1, Hybrids between Horse and Ass; 2, the Common Zebra and 
Common Ass; 3, Burchell’s Zebra and the Common Ass; 4, the 
Wild Ass (Equus onager) and the Zebra; 5, the Bactrian and Com- 
mon Camel; 6, the Alpaca and Llama; 7, the Yak and Zebu; 8, the 
Barbary and Red Deer; 9, the Rhesus and Bonnet Monkey; 10, 
the Black-fronted and Yellow-cheeked Lemurs (L. nigrifrons and 
L. xanthomystax) ; 11, Bennett’s and the Rufous Kangaroo (Hal- 
maturus bennettit and H. ruficollis). 
Among Birds :— 
12. Hybrids between the Common Canary and the following, viz. 
the Greenfinch, the Goldfinch, the Linnet, and the Siskin. 
13. Among the Galinaceous Birds, hybrids between the Com- 
mon Pheasant and the Silver Pheasant, the Gold Pheasant and the 
Bar-tailed Pheasant; also hybrids between the Common Pheasant 
and the Common Fowl, the Guinea-fowl and the Black Grouse. 
14. Hybrids between the Black Cock and the Wood-grouse ; in 
this case the offspring is termed Tetrao medius because of the con- 
stancy of this very peculiarity as regards size. 
15. Of Struthious Birds one cross only has come under Mr. 
Bartlett’s notice, namely a hybrid between the Great-billed and the 
Common Rhea. Curiously enough, this offspring was larger than 
either of the parents. 
16. Among Waterfowl a very large number might be adduced 
as evidence ; but the subjoined may suffice :— Hybrids between the 
Common Goose and the Chinese species, the Canada, the White- 
fronted, and the Barnacle Goose (indeed cross breeds amongst va- 
rious sorts of Domestic and Wild Geese have many times been observed 
by him) ; hybrids between the Common Wild Duck, the Wigeon, 
the Pintail, the Teal, and the Muscovy Duck. These and other 
instances of Waterfowl have frequently come under his notice ; and in 
all cases the afore-mentioned law applies. 
As respects fishes, authentic observations upon hybrid progeny are 
meagre ; but I may quote some experiments made at Stormontfield. 
In November and December 1857 provision was made for hatching 
