186 FISHES. 



the country in whicli they were to be acclimatised. The 

 most successful attempt of recent years is the acclimatisation 

 of the Trout and Sea-Trout, and probably also of the Salmon, 

 in Tasmania and New Zealand, and of the Californian Salmon 

 (Salmo quinnat T), in Victoria, by means of artificially-im- 

 pregnated ova. The ova were transported on ice, in order to 

 retard their development generally, and thus to preserve them 

 from destruction during the passage of the tropical zone. 



Artificial mnpregnation of fish-ova was first practised by 

 J. L. Jacobi, a native of Westphalia, in the years 1757-63, 

 who employed exactly the same method which is followed 

 now ; and there is no doubt that this able observer of nature 

 conceived and carried out his idea with the distinct object 

 of advantageously restocldng water-courses which had become 

 unproductive, and increasing production by fecundating and 

 preserving all ova, of which a great proportion, in the ordi- 

 nary course of propagation, would be left unfecundated or 

 accidentally perish. Physiology soon turned to account 

 Jacobi's discovery, and artificial impregnation has proved to 

 be one of the greatest helps to the student of embryology. 



Fishes differ in an extraordinary degree with regard to 

 tenacity of life. Some will bear suspension of respiration — 

 caused by removal from water, or by exposure to cold or 

 heat — for a long time, whilst others succumb at once. Nearly 

 all marine fishes are very sensitive to changes in the tem- 

 perature of the water, and will not bear transportation from 

 one climate to another. This seems to be much less the 

 case with some freshwater fishes of the temperate zones : the 

 Carp may survive after being frozen in a solid block of ice, 

 and will thrive in the southern parts of the temperate zone. 

 On the other hand, some freshwater fishes are so sensitive 

 to a change in the water that they perish when transplanted 

 from their native river into another apparently offering the 



