1685.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 137 



with no signs of the mouth. A layer of bhick pigmeiitum constituted 

 the eye. Membranous ridges above and below showed the first steps 

 in the formation of fins. The caudal itself was a mere membranous ex- 

 pansion of the cellular substance of the body. As such, the embryos 

 had made their escape from the eggs." 



Under Phanerodon furcatus^ page 185, Girard again mistakes the pro- 

 truding hind part of the intestine for a yelk-bag. On page 11)5, in em- 

 bryos of Holconoius rhodoterus, from three-quarters to an inch in length, 

 he speaks of this part of the intestine as " a vitelline abdominal sac." 



An examination of the figures of the Immature ovarian ova of Embio 

 tocoids has served to convince me that those figured by Dr. Girard were 

 very far from mature, and can give us but a slight conception of what 

 they are like when ripe, because he represents the germinative vesicle 

 as still cential. ^ The general rule that the nucleus breaks up aud leads 

 to the formation of a new nuclear center in an eccentric position in the 

 egg will probably be found to hold in the Embiotocoids as in otlu-r fishes.* 

 As Girard states, 1 find them embedded in the substance of the thick 

 membranes which depend from the roof of the ovarian cavity. 



The youngest foitus figured by Girard is also pretty -well advanced, 

 all of the vertical fins being already defined. The comparison also of 

 these youngest foetuses hitherto figured with some somewhat older 

 which I have had the opportunity to investigate, leads me to believe 

 that the former were much farther advanced than was supposed by that 

 author. His figures of the foetuses are poor, and give a very imperfect 

 idea of what it must actually have been possible to see. His statement 

 that the mouth 'was still closed I am also inclined to doubt, while his 

 observations on the development of the eye are simjjly calculated to 

 force a smile. He has clearly mistaken the protruding and hypertro- 

 phied hind-gut in all of his figures for a yelk-bag, the latter having prob- 

 ably vanished long before, and at a point somewhat in advance of what 

 he regards as the yelk. 



III.— The hypertrophied iiind-gut of Embiotocoid embryos 



AND ITS SUBSEQUENT DIMINUTION IN RELATIVE SIZE. 



The hypertrophied hind-gut of Embiotocoid embryos which protudes 

 into a sac-like downward projection of the abdominal profile is the 

 most important of the embryonic visceral organs. Upon opening the 

 abdominal cavity it is found that it fills up fully two-thirds of the lat- 

 ter, and that its dimensions, especially the transverse diameter of the 

 gut, is far greater than the portion of the canal which subsequently be- 

 comes the stomach. Upon cutting this swollen hind-gut open its walls 

 are found to be thickly clothed with crowded villi of the most extraor- 

 dinary length, many being entangled together at their tips, and much 



* See the law of nuclear displacement and its significance in embryology, Science, 

 i, 18^3, pp. 277, 278. 



