ZOOLOGY. 347 



pond which it is intended to stock. Finally, in order to supply these 

 little animals with an abundant aliment suited to their wants, it suffices 

 to allow to remain or to introduce into the stream or pond where the 

 fish are placed a number of frogs. The spawn of these batraehians is 

 a food which the fish seek with avidity ; and the tadpoles constitute 

 also an excellent aliment for the trouts of a more advanced age. 

 AVhen the small trouts which have been bred in this way are destined 

 to be used for stocking a river, they should be placed in the brooks or 

 small streams tributary to the river; and those streams should be 

 selected in preference which flow rapidly and noisily over a pebbly or 

 rocky bed. In proportion as the fish grow they descend spontaneously 

 to deeper waters, but do not reach them till they are sufficiently active 

 to escape by flight from the enemies they meet there Were they 

 placed immediately in the midst of other voracious fish very few would 

 escape destruction. When it is in ponds or nurseries that it is pro- 

 posed to rear the fish, care must be taken to separate totally the 

 products of each year ; for the big trouts devour the little ones, and 

 to prevent this it is necessary to keep together in the same enclosure 

 all that are of the same age. To get up, therefore, in regular style an 

 enterprise of this sort, one should have at least three ponds, from 

 which the fish should be gathered alternately three years respectively 

 after each has been stocked, and new generations placed in the pond 

 just vacated. 



M. Quatrefages states, that it is not necessary, in order to produce 

 fecundation of ^eggs, that the fish employed should be alive. M. Gol- 

 stein succeeded in fecundating the eggs of a trout which had been 

 dead four days. It is probable that the spermatic liquor also preserves 

 its virtue for a length of time after the death of the male. At any 

 rate, this is a fact which I have often verified in the case of inverte- 

 brated animals. Small fish after their exclusion are nourished for a 

 considerable length of time by the vitelline substance contained in 

 their intestines. Salmon in particular seem to have no need of other 

 aliment for a month or six weeks after exclusion. 



To the other advantages presented by the process under discussion 

 must be added that of facilitating the dissemination of the various spe- 

 cies. Our rivers, ponds, and lakes could easily be stocked with species 

 of fish, valuable either for the delicacy of their flesh or for their 

 extreme fecundity. The naturalization of foreign fish has rarely been 

 attempted, and yet the success of some attempts which have been 

 made in this direction is of a nature to encourage experiments. The 

 gourami of China has been naturalized in the ponds of the Isle of 

 France and of Cayenne. China has supplied us with those red fishes 

 (cyprinus auratux) so common in our ornamental fish-ponds. The 

 carp itself, at present so generally diffused all over Europe, is very 

 probably a native of Persia. Introduced first into Southern Europe, 

 it was not till the middle ages that the carp was carried into Prussia, 

 where it has become the object of an important commerce. This fish 

 was not known in England and Denmark till some time in the six- 

 teenth century. It was imported at a still later date into Sweden and 

 30* 



