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Size of Mouth Cavity

eggs, fish, cc, inches and volume

SIZE OF MOUTH CAVITY.

While this, of course, varies with the size of the fish, it is always large, since the head of this fish is much larger in proportion to the size of the body than is generally the case in teleosts. This may be easily seen by turning to plate 1, figure 1; to the dorsal view of the head, plate i, figure 3; and to the figure showing the mouth with embryos, plate m, figure 7.

Incubating males vary greatly in extremes of size. The smallest ever taken by the writer was 13 inches long over all and carried 4 eggs; while the largest was 23 inches in extreme length but carried no eggs. However, the condition of his hyoid region indicated that he had just given up or was about to receive eggs. The largest number of eggs taken from one male was 55, the fish being 22 inches long. However, the average size of adult egg-carriers is remarkably uniform, running from 18 to 21 inches. On the other hand adult breeding females run larger, from about 19 to 24 inches.

Casts were made of the buccal cavities of 5 nursing males, and 4 of these will now be described seriatim. The first, a cast of plaster of paris, with a volume of 140 c.c., was made from an 18-inch male. The second, also of plaster, is of the mouth of a male 18.75 inches long carrying 11 eggs. Its volume is 135 c.c. The third, of the same mate rial as the preceding, was at the time thought to be the maximum of size since it had a displacement of 267 c.c. Unfortunately the notes giving the size of the fish and the number of eggs carried have been lost. However, these may easily be omitted since full data can be given for the fourth fish, the one from whose mouth 55 eggs were taken.

This fish (22 inches long) was brought to the laboratory that a plaster cast of its enormous "Keimhole" might be made, but there was not enough plaster in the laboratory to fill it, and there was none in Beaufort. In this predicament the director of the laboratory, Mr. Henry D. Aller, came to the rescue with the suggestion that a cast be made of Portland cement, a barrel of which was at hand. This was done and the fish was held with a towel wrapped around its gills to prevent the escape of the semi-liquid cement until it had hardened. The head was then cut off and put in a dense cedar thicket under a box where it remained until the ants had eaten off all the flesh. Then the cast was carefully freed of the disarticulated bones, shel lacked and preserved.

This cast, shown in dorsal, lateral, and ventral views in figures 4, 5, and 6, plate II, is enormous, exceeding in volume both the next largest taken together. Immersed in water up to the deep insinking made by the sphincter muscles of the oesophagus, its displacement is 580 c.c. The volume of the average-sized egg is 3.75 c .c. Fifty five eggs would have a total volume of 206.3 c.c. Allowing one-third of this additional for the interstices between the eggs, the total space occupied by the eggs was 275 c.c., leaving 315 c.c. not occupied.

The mouth-cavities of the fish carrying these eggs were very large to begin with, since, as has been noted, the head makes up a large part of this catfish, and these cavities were still further enlarged to accom modate the considerable numbers of immense eggs carried therein. Careful dissections have brought to light the following points: (1) the gill-covers, while outwardly showing no very marked distention, inwardly stand out and away from the gills by about half the diameter of an egg; (2) the gill-arches are pushed outward, giving them a sharp boomerang-like bend in the center; (3) the hyoid cartilages are greatly depressed, forming an outpushing which has been elsewhere referred to as a "double-chin" as shown in the drawing of this fish, figure 2, plate 1; (4), that part of the buccal cavity, behind the pharyngeals and back of the last gill-arch, extending to the point where the sphincter muscle shuts off the oesophagus, is of considerable volume, and in it are always to be found the last eggs, which are always more or less hard to extract. This was particularly noted in the season of 1909. The males could be held up by the tail and shaken without setting all of the eggs free. In a large fish there is space enough back of the last gill-arch for a number of eggs to be held snugly by the mucous lining of the pharynx.

The above measurements, while accurate enough for the caste, can only approximately give us the sizes of the buccal cavities of these fish. That some error is to be discounted is clear from the process of making the casts as given on page 34. The plaster casts are probably too small, owing to too great constriction in the opercular region; while the cement cast is probably somewhat too large, owing to the distention caused by the large amount of heavy cement.