January 8, 1886 ] 



27 



through the faucet i, the water rising to the level 

 of the line a, before the capacious outlet siphon s 

 begins to operate. This siphon, through which 

 the water runs out of the trough faster than it 

 conies in at *, soon brings the water down to the 

 level of the line b. when the siphon takes in air 

 and ceases to operate, after which the trough 

 again slowly fills up with water to the level of the 

 line a. This process is repeated automatically, 

 and as long as the water is permitted to flow 

 through the device. It requires ten minutes for 

 the water to rise or fall from the one level to the 

 other ; and, since the jars have only a cloth tied 

 over the mouth below, the water rises and falls to 

 the same extent in them. This very slow and 

 gentle rise and fall of the water in the jars and 

 trough have been found sufficient to aerate the 

 eggs, and give them all the movement they need. 



The majority of the eggs in this contrivance 

 float at the surface. Some, of course, remain sus- 

 pended below the surface ; but an exceedingly 

 small percentage of the eggs ever sink and die, as 

 in almost all of the other forms of apparatus 

 hitherto used. The result is that the mortality is 

 probably under five per cent, — a percentage of 

 loss not greater than that experienced in the 

 most successful treatment of shad ova. 



The freshly fertilized ova, treated with an 

 abundance of good milt, are introduced into the 

 hatching-device through the hole in the centre of 

 the bottom of each jar by means of a glass funnel. 

 Beyond an occasional siphoning-off of the sedi- 

 ment on the bottom of the trough and the cloth 

 covers of the jars, the eggs require no attention 

 until hatched. 



Heretofore great mortality has been caused by 

 the use of metal in the construction of the hatching- 

 vessels and strainers. Since the adoption of glass, 

 wood, and cloth as the only materials used in the 

 construction of the hatching-apparatus here de- 

 scribed, combined with the very gentle movement 

 to which the eggs are subjected, complete success 

 has been attained. The eggs oscillate up and 

 down through a space of only five inches from 

 the level of a to that of b, and, withal, so gently 

 that they suffer no hurtful shocks of any kind 

 whatever. Captain Chester's device will doubt- 

 less be used with great advantage in the propaga- 

 tion of the Spanish mackerel. In twenty-four 

 hours the latter would be ready to be set free 

 from the apparatus ; whereas it requires eleven 

 or twelve clays to hatch the eggs of the cod, with 

 the temperature of the water ranging from 45° to 

 48° F. 



Each of the jars J is seventeen inches high by 

 nine inches in diameter, and will hold from one- 

 half to one million of cod-eggs ; so that an ap- 



paratus of the style shown above, and occupying 

 not much over a square yard of space, would 

 accommodate from two to four millions of ova. 

 in four jars. 



These experiments show that violent movement 

 of the eggs of the cod is of no advantage ; that 

 such movement is, on the contrary, injurious, if 

 not mortal, when continuously maintained. The 

 requisite conditions for successful hatching of this 

 important food-fish having been settled, the great 

 station of the fish commission at "Wood's Holl af- 

 fords unlimited opportunities for conducting the 

 work for at least three months of the year, during 

 which time from five hundred to one thousand 

 millions of eggs might readily be hatched out by 

 the aid of the Chester apparatus, and set free in 

 the adjacent waters. 



Since my arrival here, I have observed, that, 

 some days after hatching, the larval integument 

 over the head of the embryo cod is raised more 

 and more from the top and sides of the brain. A 

 spacious serous cavity is thus formed over the 

 brain ; so that, when the embryo is viewed frcm 

 the front, it seems as if it bore a sac on the head 

 almost as large as the yelk-bag formerly had 

 been, attached to the top and sides of the head. 

 On account of the fact that the young larvae of 

 the cod seem to delight to remain near the sur- 

 face, it has occurred to me that this vesicular 

 sinus above the brain is of use in buoying the 

 young embryos up after they have escaped from 

 the egg. That this is actually true, I have every 

 reason to believe from the circumstance that 

 embryos a few days old never rest in the water 

 in a horizontal position, but with the head upper- 

 most, and the tail slanting backward and down- 

 ward from it at an angle of 45°. When swim- 

 ming, they move horizontally ; but at once, upon 

 coming to rest, the young fish assumes a slanting 

 attitude, the tail dropping down into the inclined 

 position, while the head is thrown up. The large 

 sinus here described was first observed by me, in 

 a less developed condition, on the head of the em- 

 bryo Spanish mackerel in 1880. The space in this 

 sac in that species I called the supracephalic 

 sinus. 



Since the foregoing was written, we have dis- 

 covered that the specific gravity of the sea-water 

 has a great deal to do with the healthy develop- 

 ment of the eggs of the cod. By accident a 

 broken valve admitted some fresh water to our 

 salt-water tank, causing the specific gravity to 

 fall from 1.0256 to 1.021 or 1.022. In this density 

 the eggs immediately sank, causing us to lose 

 over two millions. After this unfortunate ex- 

 perience, and also judging from the fact that 

 ever since the break in the valve has been 



