OP ARTS AND SCIENCES. 25 



ance at very different times in the many species we have examined. 

 Hence, until the characteristic pigment pattern of an embryo is pretty 

 well known, it is easy to confound the eggs of very different species. 

 The position and shape of the otoliths and the degree of develojjment 

 of the pectorals become also excellent guides to the identification of 

 eggs well advanced in their development. The differences in the 

 young embryos on hatching are very considerable, and in these earlier 

 stages the degree of development of the head, the proportional size of 

 the yolk-bag, the shape of the embryonic fin, the position of the Vent, 

 and the pattern of the pigment spots, are all of great use in the identi- 

 fication of the species. 



It is remarkable that no monstrosities have ever been picked up 

 among the large number of pelagic eggs examined during the past 

 twenty years, while among the eggs raised by artificial fecundation, 

 the number of eggs which do not develop is very considerable. It is 

 true, that unfertilized eggs, after a day or two, probably fall to the 

 bottom, and are rapidly decomposed, or eaten by other animals. As 

 the majority of the species of Flounders, of which the pelagic eggs 

 have been found, live together in considerable numbers, it is probable 

 that at the time of fecundation but few eggs escape being fertilized : 

 the same is the case with Ctenolabrus, Tautoga, and other shallow- 

 water species. The pelagic eggs are, of course, at the mercy of the 

 winds and waves, and are found in the greatest abundance in the 

 streaks formed by tidal eddies and by winds, which are everywheie 

 on the sea-coast such excellent collecting ground for embryos of in- 

 vertebrates and for other pelagic animals. 



We have collected at Newport the pelagic eggs of six species of 

 Flounders, two species of Cottus, those of Ctenolabrus, Tautoga, 

 Osmerus, and Lophius, and have in collection the eggs of ten species 

 of fishes as yet not determined ; but they are probably the eggs of 

 Motella, of Labrax, of Poronotus, and of the Bluefish. The exact 

 identification of these eggs must be deferred to another season. 

 Several of the eggs have been referred to the species of Flounder and 

 other young fishes which were figured in former papers of Mr. Agassiz 

 in the Proceedings of the American Academy of Arts and Sciences. 



The presence or absence of an oil globule is an excellent guide in 

 the identification of the egg; the size of this globule is, however, 

 quite variable. In one of the species of Cottus there are many glob- 

 ules present, and the number of these varies from sixteen to thirty-two 

 for this species. In another species, Hemitripterus, in which there is 

 generally only one globule, it is not an uncommon occurrence to find 

 two globules. 



