THE FLOUNDER FAMILY. 323 



the surface, but not all, since these are visible in almost every 

 example up to the period of hatching. A very different 

 condition prevails in certain viviparous fishes as described by 

 Eingemann 1 in which a shrinking of the yolk occurred so as to 

 form a breathing-chamber after leaving the ovarian follicle. 

 Many of the eggs had groups of minute fatty granules dotted 

 all over the yolk, as shown in the figure. Next day (22ud 

 March), at 12.30, considerable progress had been made, the disc 

 being in the mulberry-condition, the cells of the blastoderm 

 being often prominent, and at 5.40 P.M. much more finely 

 divided. The said minute granules of oil occur over the yolk, 

 beneath the protoplasmic investment, and they appeared to be 

 fewer next day, so that probably they were gradually used up 

 in the progress of development. The minutely cellular disc 

 presents an inward curvature at its edge, which is not quite 

 regular from the occurrence of minute projecting cells. The 

 disc does not always occupy the centre of the yolk under 

 examination. Occasionally a group of large oleaginous globules 

 lies under the developing disc not at the uppermost pole of 

 the egg. 



On the 24th, the embryo was outlined with the optic 

 enlargements. The blastopore in some was almost closed, and 

 Kupffer's vesicle was represented by a few granules or minute 

 vesicles. The notochord formed a pale streak extending forward 

 to the middle of the trunk, and the margins of the body were 

 faintly indicated. 



Next clay the blastopore had closed, and Kupffer's vesicle 

 was large. Numerous muscle-plates had formed, and the 

 notochord could be traced forwards almost to the head. On 

 each side a delicate cellular border stretched backward outside 

 the muscle-plates. The granules had now disappeared from 

 the surface of the yolk. 



On the 26th March, the embryo resembled Holt's fig. 58, 

 PI. VIP, and traces of blackish pigment appeared along the 

 body, best seen by placing white paper beneath the specimens. 



1 Vivip. Fishes. Bullet. U.S. Com. 1892 (1894) p. 421. 



2 On the Eggs, larval and post-larval stages, of Teleosteans. Trans. Roy. 

 Soc. Dub. v. 



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