388 Professor W. C. Mcintosh [Feb. 1, 



injured, the tube was set aside. Some days afterwards, wbeu ex- 

 plaining the nature of the experiment to Prof. Ewart, be noticed 

 motion in tbe tube, and further examination showed that after all this 

 exposure to heat the little flounders had emerged as usual, and were 

 alternately floating and swimming about in the water. On the other 

 hand, severe frosts are fatal to ova crowded in shallow vessels, in 

 many cases actual rupture taking place ; * and the same occurs in 

 large eggs, for example those of the catfish, deposited on the bottom 

 of the vessel. 



Out of the little glassy sphere, after a longer or shorter interval 

 (varying from a few days to a few weeks, according to temperature), 

 comes a minute and nearly transparent fish (Fig. 2) which at first is 

 often as passive in the currents as the eggs themselves. f It soon, how- 

 ever, uses its tail for swimming and its pectoral fins for balancing. 

 Its shape is somewhat like that of a tadpole, partly from the large 

 head, but mainly from the great size of the yolk-sac, which contains 

 a store of nourishment on which the little mouthless creature, about 



Fig. 2. 



Larval Ling, immediately after hatching. 



3 mm. long, sustains itself for a week or ten days. In this respect it 

 somewhat resembles the young salmon in which a much larger 

 collection of the same food supports it about six weeks amongst the 

 gravel in the spawning-bed of the river, though a closer scrutiny 

 reveals certain essential differences. Thus the store of nourishment 

 in the yolk-sac of the salmon is taken up by the bloud-vessels which 

 branch in a complex manner over the whole yolk, whereas in the 

 young cod, though tlie heart is present and pulsating, not a blood- 

 vessel at first is seen, and none ever enters the yolk-sac. The 

 absorption of this nourishment therefore must take place by aid of the 

 cells and tissues themselves, and there is nothing specially wonderful 

 in this, when the conditions in the endoderm of Hydra, and other 

 instances of intracellular digestion are considered. 



It has been mentioned that these minute and most delicate little 



* ' Nature,' June, 1886. 



t For some years tlie development of fishes has been studied by able workers, 

 amongst others on the Continent, by Gotte, Kupflfer, Hoffman, Henneguy, E. 

 Van Beueden, 0^jannikov, and Rafaele; in America, by Alex. Agassiz, Kyder, 

 and Whitman ; while in our own country, Ransom, Klein, Cunningham, Prince, 

 and Brook have carried out similar researches. 



