26 PROCEEDINGS OF THE AMERICAN ACADEMY 



Closely allied species of Floimders are found to have eggs either 

 with or without an oil globule. The question naturally arises how 

 far in one and the same egg the number of globules may vary. I 

 have followed an egg in which in some stages the number of globules 

 varied in number from day to day. These pelagic eggs all appear to 

 have a great number of minute fatty globules scattered through the 

 yolk mass ; these may or may not unite in a single or in many glob- 

 ules, or may always remain scattered in the yolk. It is undoubtedly 

 to Clie presence of these minute fatty globules and the larger oil glob- 

 ules that the pelagic eggs owe their capacity for floating. Many 

 pelagic eggs undoubtedly sink in the latest stages of growth. 



The number of these pelagic eggs is very great. Hardly a day 

 passes when the fishing with the surface-net does not bring in a num- 

 ber of eggs. The spawning season of many of the fishes which lay pe- 

 lagic eggs is not very long : at any rate, the different eggs succeed one 

 another quite rapidly, and of the twenty-one species of pelagic egg3 

 thus far observed at Newport, none extend over a greater period than 

 six weeks. The statement I had made, that the eggs of Ctenolabrus 

 were found during the whole summer, rests on the incorrectness of the 

 identification of pelagic eggs closely resembling those of Ctenolabrus, 

 and which are collected in the last part of July and during August. 



As the data for the exact determination of some of these eggs are 

 still incomplete, we defer publishing them until they can be supple- 

 mented with the observations of another season. 



During the summer of 1883, our attention was directed mainly to 

 the earlier stages of development, embraced between the fecundation 

 of the egg and the complete formation of the embryo. The numer- 

 ous researches on the embryology of the teleostean fishes leave many 

 points of fundamental importance yet to be settled. In evidence of 

 this, we need only refer to the parablast theories that have appeared 

 since the investigations of His ; the contradictory views concerning 

 the origin of the so-called "free nuclei" which appear beneath the 

 blastoderm, and the part they play in building up the embryo ; the 

 controversies relating to the manner in which the embryo is formed ; 

 and the widely different views respecting the origin of both the meso- 

 derm and the entoderm. Kupffer's vesicle still remains a complete 

 mystery ; and no one has thus far succeeded in giving a complete and 

 satisfactory account of the origin of the germ-ring (" embryonic rim," 

 Balfour). 



No attempt has been made to explain how the alimentary canal is 

 formed ; and the precise origin of the chorda and its mode of differ- 



