3ço Memoirs of the Indian Museum. [Vol. V, 



The hyoid arch has a curved shape, and the arches of both sides meet ventrally. 

 At their point of junction is to be seen a small cartilaginous piece (probably 

 basihyal) projected forwards, — its hinder portion meeting the anterior prolongation 

 of the basibranchial. The various divisions of the arches are not yet differentiated. 

 The cartilaginous cranium is formed and is still more or less transparent. The heart 

 may be faintly made out, as before, beneath and behind the basibranchial cartilage. 

 The gas-bladder takes an elongated shape, and its dorsal surface is deeply pigmented 

 black. Its anterior prolongation becomes indistinct, but its posterior prolongation is 

 quite distinct, and it seems to open just behind the anus by a distinct slit. The noto- 

 chord is well developed, and is constricted off into a number of pieces, to form the 

 beginning of the future vertebral column. The skeletogenous layer has started its 

 work, and the skeletogenous cells may be seen in large numbers just at the base and 

 above the notochord. In the latter place they are quite abundant, and may be seen 

 to enclose the spinal cord. The heterocercal tail is fairly well developed, but the 

 fin-rays have not yet made their appearance. The myotomes are well developed, 

 and the transparency of the body is still to a large extent retained. The alimentary 

 canal seems in some places to consist of a solid cord of cells, and the cavity is 

 obliterated, but this may be due to external causes. 



The liver may be seen as a thick mass of cells, in front of the stomach. The 

 big stellate chromatophore still persists, though it is now much reduced in size. In 

 addition to it, a number of small chromatophores (about 16) make their appearance 

 on the ventral side of the body. The fin-folds are still continuous, though much 

 norrowed towards the caudal end. 



Stage V (pi. xviii, fig. 4). This stage is much more advanced than stage IV. 

 The intermediate stages which would have been very interesting are missing. The 

 snout or beak does not seem to have kept pace with the enormous increase in the 

 length of the body. In fact, I tried to establish a ratio between the length of increase 

 of the body, the gas-bladder and the beak, but failed hopelessly. The above table 

 (p. 388) will show that the increase in the length of the beak has no relation whatsoever 

 with the development of the body. 



The operculum is well developed and the branchial arches can only be indistinctly 

 made out. The papilla-like outgrowths have reached a considerable size and are quite 

 a characteristic feature of this stage. The cranium is fairly well developed, and its 

 transparency is lost. The gas- bladder has kept pace with the increase in length of the 

 body and the same is the case with the alimentary canal. The position of the gas- 

 bladder in the body is now denoted only by a long series of deeply pigmented bodies 

 close beneath the notochord. On a careful examination under the high power of the 

 microscope a dense network of capillaries may be seen lining the walls of the gas- 

 bladder. These capillaries probably form the ' ' retia mirabilia "or " red bodies ' 

 of the adult. The}^ are arranged in fan-like tufts over almost the whole extent of the 

 inner surface of the gas-bladder. Owing to the opacity of the body the notochord is 

 not distinctly visible, but it is being gradually enveloped by the skeletogenous cells 

 to form the future vertebral column. The condition of the tail is midway between 



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