9 6 



AMERICAN 



mortification, every one of them spoiled. Nothing daunted, he ex- 

 amined the temperature of the brook, and found, not only that it was 

 13 below that of the river (6'2 to 75,) but that it varied 12 from 

 night to day. This gave the clue to success. Taking a rough box, 

 he knocked the bottom and part of the ends out, and replaced them 

 by a wire gauze. In this box the eggs were laid, and it was anchored 

 near shore, exposed to a gentle current that passed freely through the 

 gauze, while eels or fish were kept off. To his great joy, the minute 

 embryos were hatched at the end of sixty hours, and swam about the 

 box, like the lavse of mosquitoes in a cask of stagnant water. Still, 

 though the condition of success was found, the contrivance was still 

 imperfect ; for the eggs were drifted by the current into the lower 

 end of the box, and heaped up, whereby many were spoiled for lack 

 of fresh water and motion. The best that this box would do was 

 ninety per cent., while often it would hatch only seventy or eighty 

 per cent. 



The result was a triumph. Out of 10,000 ova placed in this con- 

 trivance, all but seven hatched ! In spite of these delays, and of the 

 imperfect means at hand for taking the fish, Green succeeded in 

 hatching, and setting free in the river, many millions of these tiny 

 fry. 



In confinement they cannot be kept, because the yolk-sac does not 

 suffice for their support for more than one or two days. But care 

 must be taken to liberate them in a. safe place. Green observed that, 

 on setting them free among the shallows near shore, the dace (Argy- 

 reus) and other little fishes rushed to the spot, and commenced jump- 

 ing at them. In the stomach of a dace he found fourteen shad fry. 

 Then, by a series of most ingenious experiments, he discovered that 

 the fry, so far from frequenting the shallows, like many minnows, 

 made directly for the main current, in mid-river. How different 

 this from the young trouts that lie almost helpless for forty-five days, 

 and then are fain to hide behind stones and roots ! Whereas, these 

 minute, transparent, gelatinous things push boldly for the deep, 

 swift current, where they are too insignificant to be attacked by the 

 great fishes. 



So the fry must be let go in the proper way by towing the boxes 

 into mid stream, or by liberating them during the night, when their 

 enemies do not feed. 



The ovaries of a full-grown shad (Alosa praestaMlis) weigh at the 

 spawning season about thirteen ounces, without the membranes. 

 With a common lens, three sizes of ova are at once distinguished. 

 The first have a diameter of 8-100ths to 9-100ths of an inch. These 

 are transparent and ready to be laid ; the second, 4-100ths to 5-100ths 

 of an inch ; the third, 2-100ths of an inch. These two smaller sizes 

 are opaque ; they are still found after the fish has spawned, and are 

 the crops ready to mature the next year and the year after. This 

 state of the ovary has its parallel in the turtle, and possibly in all of 

 the vertebrata. 



