THE HISTORY OF FISH-CULTURE. 501 



During the period of incubation, tlie spawn requires the greatest care. 

 The washing of the eggs immediately after the fecundation is rather 

 difficult on account of their delicate outer skin, and this is precisely the 

 time when they mnst be cleaned from all impurities ; for the development 

 of parasites is fatal to them at this time. The cleaning of the spawn is 

 done by means of the down of a quill or with a soft brush ; the spoiled 

 eggs, which can easily be recognized by their pale-yellow color, are 

 picked out with pincers similar to those used in anatomy, but differing 

 in this respect that, instead of being denticulated, they terminate in a 

 cavity which seizes the spoiled egg without endangering the others. If, 

 on account of too strong a current of water, the spawn gets piled up in 

 one place, which ought to be avoided, we must immediately diminish the 

 current and spread the spawn evenly over the whole bottom ; using 

 for this small glass tubes, which are made in the following manner : 

 take a tolerably large glass tube, blow a globe at one of its ends, and 

 draw out the other end to a fine point ; the large opening is closed by 

 a stopper pierced lengthwise, through which a thin glass tube is passed. 

 In using the tube, stop with the finger the thin end, and direct the 

 the tube which passes through the stopper on the spawn, which, as soon 

 as tfie finger is raised, jjasses rapidly, at the same time with the water 

 into the globe of the tube. 



This instrument can be used not only for transporting spawn, but also 

 for taking hold conveniently of small newly-hatched fishes. 



6. — DEVELOPJIENT OF THE EMBRYO AND THE HATCHING OF FISH. 



The egg of a fish is composed of an inner bladder, which, as long as the 

 egg is not put in the water, is in intimate contact with an outer cover- 

 ing. The inner bladder and its covering are joined by a thin channel, 

 which, on the outside, opens by an orifice called micropyle, through 

 which the spermatozoids enter the eggs. This opening was first dis- 

 covered on the egg of a small bream {Ahramis hlicca, C.) by a Eussian 

 scientist, Mr. Baer, of the Imperial Academy of Sciences of St. Peters- 

 burg, and was next observed on the trout, the salmon, and the pike, &c. 

 As soon as the egg has been brought in contact with milt diluted in 

 water, or simply with pure water, the outer covering swells, through 

 endosmosis, and separates from the coating of the inner utricle. Dur- 

 ing this absorption of water through the outer skins of the egg, it is 

 absolutely necessary that a spermatozoid with fecundating liquid should,, 

 through the micropyle, pass inside the bladder. If this is not the case, 

 no fecundation takes place. During the separation of the outer skin of 

 the bladder, the channel intended to introduce the spermatozoid into 

 the egg breaks, and communication between the bladder and the outside 

 is interrupted; so that, if the spermatozoid has not had time enough to 

 penetrate into the bladder, it cannot possibly get into it afterward, and 

 the egg remains barren. These observations prove that it is very 

 important that the spermatozoids of the milt, diluted in water, should be 



