OF ARTS AND SCIENCES. 289 



IX. fig. 5) the general pattern is similar to that of the adult. In 

 subsequent stages the spiny processes of the operculum are developed 

 as well as those of the large ray of the ventrals. The ventrals make 

 their appearance at about the time of the disappearance of the yolk 

 bag (Plate IX. fig. 3), somewhat later than the formation of the rudi- 

 mentary anterior dorsal spine (Plate IX. fig. 2). The outline of 

 the young fish becomes more compact with age, passing gradually 

 through the changes represented in Plate IX. figs. 1-5, from an 

 elongated slender fish to one with a comparatively broader and 

 stouter body. 



Pelagic Fish Eggs. 



The number of species of marine Fishes of which the eggs are 

 pelagic is probably quite large. Scarcely a summer passes without 

 some new egg being brought to light by the surface-fishing carried on 

 at Newport. The eggs of the majority of our species of Flounders, 

 those of Ctenolabrus, of Tan toga, of several species of Cottus, I know, 

 from my own observation, to float on the surface of the water. 

 Hackel has called attention to the pelagic eggs of Lota or some 

 Gadoid which he had observed as early as 1866. Sars has shown the 

 same to be the case with the eggs of the Cod. Mr. Ryder has figured 

 the eggs of the Spanish Mackerel (Bull. U. S. Fish Com., i. PL) Both 

 he and E. van Beneden, who also has observed pelagic fish eggs 

 (Quarterly Journal Mic. Soc. 1878), have called attention to the 

 value of these pelagic fish eggs for embryonic investigations. Mr. 

 Ryder has also made observations of the spawning of Zeus, and 

 suggests that many of the marine Fishes are nocturnal spawners. 

 That this is the case with many of the Fishes I have named above 

 seems probable from the state of segmentation in which they are found 

 to be on the morning following the day on which they were collected. 

 The pelagic eggs collected during the day were invariably well ad- 

 vanced, and the experiments for artificial fecundation which I have 

 made with Ctenolabrus and Tautoga to obtain the very earliest stages 

 of the development of the egg were invariably made late in the after- 

 noon, towards dusk. I have long known the eggs of Lophius to occur 

 floating on the surface as a gigantic mucous band, and they have also 

 been subsequently collected by the U. S. Fish Commission. The eggs 

 of Fierasfer are also pelagic ; see Emery's monograph. I have my- 

 self also collected the eggs of the Spanish mackerel on the surface, 



VOL. XVII. (n. S. IX.) 19 



