XXVI INTRODUCTION. 



A few observations on the impregnated roe may be worthy 

 attention. Dr. Walker of Edinburgh, in an essay on the 

 Natural History of the Salmon, published in the Transac- 

 tions of the Highland Society, quoting the experiments of 

 Jacobs of Berlin, says, he found that when the spawn of both 

 sexes were extracted from dead fishes, the ova by mixture 

 can be fecundated by the milt ; and when placed under water 

 in a proper situation can be brought forth into life. He 

 further discovered that this artificial fecundation can be ac- 

 complished with the roe and milt of fishes which have been 

 dead two and even three days. This appears to point out 

 the mode of obtaining the fishes of neighbouring countries 

 by the transportation as far as possible of the living gravid 

 fishes, afterwards for a time while dead, and finally by the 

 mixture and further transportation of the mixed roes. 



But there appear to be other, and still greater facilities. 

 Mr. Jesse states, that he has been assured by persons who 

 have lived many years in the East Indies, that ponds which 

 become perfectly dry, and the mud hard, have after the rainy 

 season been found with fish in them, although no stream 

 communicated with them, or any passage or other means by 

 which fish could be admitted. This curious fact has been 

 confirmed to me by Colonel Sykes and other observers who 

 have lived long in India, who state that the tanks and ditches 

 near fortifications are alternately filled and empty on the oc- 

 currence of every rainy and dry season, but that a few days 

 after the commencement of each rainy season these tanks and 

 ditches are replenished not only with water, but also with 

 small fish. The solution appears to me to be this. The 

 impregnated ova of the fish of one rainy season are left un- 

 hatched in the mud through the dry season, and from their 

 low state of organization as ova, the vitality is preserved till 

 the occurrence and contact of the rain and the oxygen of the 

 next wet season, when vivification takes place from their joint 



