122 THE EVOLUTION OF LIVING BEINGS. 



mes by Herla and Zoja (cf. Biol. CBl. 1912 p. 718), of 

 Arthropoda it is well known, that in the group of the 

 insects such hybrids are common. Among MoUusca 

 HeUx hortensis and H. nemoralis frequently cross, 

 while among Pisces it is well known that f . i. in the ri- 

 ver IJssel in Holland every hoal of the big nets called 

 ..blessings" (not from the fish's standpoint!) contains 

 hybrids between the genera Leuciscus and BUcca, 

 while hybrids between BUcca and Abramis and be- 

 tween different Linneons of Leuciscus are common in 

 many rivers. It appears that generally hybrids be- 

 tween different Linneons of fishes are by no means 

 rare (cf. Claus). Among .4 m/>At6«fl natural hybrids be- 

 tween different Linneons of Triton are known (cf . PoU. 

 Biol. CBl. 1909 p. 30) and also between different Lin- 

 neons of frogs (cf. Boulenger). Among Aves hybrids are 

 especially common between different Linneons, yes 

 even between different genera f . i. of ducks, even such 

 between individuals belonging to different famiUes 

 viz between Penelope (fam. Cracidae) and Phasianus 

 colchicus (cf. Haecker p. 211) but this one not in 

 nature. In Sweden Birkhahn and Auerhenne cross 

 frequently, probably because the Auerhahne are 

 decimated by shooting (cf. Naumann Naturgesch. 

 der Vogel Mitteleuropas. Vol. 6 p. 106 Anm. 13.108. 

 Among Mammalia, Darwin says in the Origin p. 224, 

 that he has reason to beUeve that the hybrids from 

 Cervulus vaginahs and Reevisii are perfectly fertile. 

 So are the Indian humped and common cattle when 

 crossed. 



Among plants, hybrids between different Linneons 



