HYBRIDS. 47 



fertility graduating from sterility to perfect fertility : and what occurs in other 

 divisions of the vertebrata has been shown to likewise take place in fishes. Pallas 

 held that in some instances domestication tends to the elimination of sterility : 

 while Morton considered that it merely evolves the capacity for being prolific. 



Evidence has been handed down to us from early times that the existence of 

 hybrid fish was believed in, as may be seen by referring to Willoughby and 

 Ray in 1686, while Pennant (Brit. Zool., 1812) alluded to " hybrid fish, for that 

 such exist, those persons who had paid most attention to the subject in ichthyo- 

 logy have not a doubt." 



The ova of these fishes have to be fertilized by the milt of the males diffused 

 as a rule in the surrounding water, and it may occur, especially in streams, that 

 milt comes in contact with, and perhaps fertilizes, the eggs of a female of a different 

 species, genus, or family, thus giving rise to a hydrid offspring.* But the size of 

 the micropyle of the ovum, and that of the spermatozooid of the milt, must be of 

 conforming capacities, or fertilization would be a physical impossibilty. 



of domestic cattle, and numerous hybrids were born, nine males, and ten females ; of tbese, the 

 older ones of both sexes have already {Field, Jan. 15, 1885) been used for further experiments. 

 Females on being paired with an ordinary European bull, in every case proved fertile, so far conclu- 

 sively proving the fertility of the hybrid Gayal cows when paired with European bulls of unmixed 

 blood. But the hybrid Gayal bulls, without exception, have proved absolutely sterile although 

 they have readily paired both with hybrid females and cows of umnixed European races. 

 Likewise, it was remarked (Field, May 16th, 1885) that the same experimenter, Professor Kuhn, 

 has also crossed the domestic sheep with the moufflon, Ovis mmmon, the wild sheep of Corsica and 

 Sardinia. The results were equally favourable with the various European, Asiatic, and African 

 breeds of domestic sheep and uniformly successful, whether ewes of the domestic sheep were 

 crossed with moufflon rams, or the reverse. Their descendants proved fertile in both instances when 

 crossed with each other. This was the case with animals of close consanguinity and even with 

 twins, and in (1885) lambs of mule crossings have been born which belong to the fourth 

 generation of these animals crossed exclusively between themselves. 



Among birds, Eyton crossed the Chinese goose with the common goose, from which he reared 

 two hybrids, but from separate sittings; while from these two hybrid offspring he obtained a 

 hatching of eight hybrids, the grandchildren of the original unmixed parents. Darwin procured 

 two of these hybrids, and from them (brother and sister) raised five extremely fine birds from two 

 hatches, which in every respect resembled the hybrid parents. Pheasants, also, are known to 

 cross freely. In this class, kept in confinement, many interesting facts on this subject have been 

 recorded, and which seem to have more analogy to what obtains in fishes than the instances 

 observed in the higher grade of mammals. Hybrids have been raised from a hen Canary and 

 a cock Goldfinch : from a hen Canary and a cook Siskin, the young of this cross resembUng 

 the Siskin in shape : from a hen Canary and a Linnet. Most of the foregoing have proved fertile, 

 and no great trouble has been experienced in inducing the parents to pair, but the difficulty 

 increases in proportion to the remoteness of the relationship between the species. A hen Canary 

 has also been crossed with a Bullfinch, but the eggs, says Bechsteiu, seldom prove fruitful ; still 

 Dr. Jassy found a plan of making other Canaries sit on the eggs and bring up the young. A hen 

 Canary paired with a Nightingale in Beohstein's presence, but the eggs did not hatch. The reason 

 why the Canary has been selected as the mother is, because she will lay her eggs in an artificial 

 nest, which wild birds are not readily induced to do. Some, at least, of the foregoing hybrid 

 progeny of birds were fertUe — as crosses between hen Canaries and Goldfinches, Siskins and Green- 

 finches. The first eggs of these hybrids were said to be very small, and the young hatched from 

 them very weak, but the eggs of the next season were larger and the nestlings stronger and 

 stouter. 



* Leuchart observed that, " if, however, it be true, as Fraisse asserts in his work on Scientific 

 fish-hreeding — and we have no ground on which to doubt it, prima faoie — that he has been able to 

 effect, by artificial fecundation, a hybrid offspring between the brook trout and the burbolt, which 

 is between two forms which belong to two totally different groups, then the limits of hybridization 

 must be greater than we have hitherto been inclined to assume." In the bulletin of the United 

 States Fish Commission for 1882 is an account of a hybrid between a fish belonging to the herring 

 JEamily, an Alosa or Clnpea, which furnished the eggs, and the striped bass, Eoccus lineatm, that 

 pertains to the perches, and which supplied the milt. (Some doubts have since been thrown on 

 the latter experiment, it having been questioned whether fertilization took place as described, 

 and the young were not kept, while the first seems to require confirmation). 



Passing on from instances of hybrids which have been recorded as bred between fishes belong- 

 ing to distinct families, we come to intercrossings effected between species belonging to two 

 different genera. Livingston-Stone observed in 1869 how he had artificially crossed the eggs of 

 the yellow perch, Perca flavescens, with the milt of a glass-eyed perch, Luciopena, both 

 pertaining to the perooid family. The embryos continued to develop until the seventh day, when 

 all at once they ceased to do so. Mr. Eoosevelt, Proc. Amer. Assoc, for Adv. of Science, 1884, 

 recorded that in the United States Salmo confinis had been bred with the white fish, Coregonus 

 albus; the brook trout with the fresh- water herring, Coregonus clupeiformis ; the brook trout and 



