Oral Gestation in the Gaff-Topsail Catfish, Felichthys Felis. 36 



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 

 I ; (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 casts, 

 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. 



SIZE OF EGGS AND THE NUMBER INCUBATED. 



The eggs, while enormously large, show considerable variation in 

 size, running from 15 to 25 mm. in diameter. Heretofore, however, 

 sufficient measurements have not been made to enable one to say 

 with any definiteness what is the size of the average egg of any oral 

 gestator. For the gaff-topsail hundreds of measurements have been 

 made and from them the following diameters are given as covering 

 both normal and abnormal sizes of eggs. It has been constantly 

 observed that the non-fertile eggs of this fish are much larger than 

 the fertile ones. In 1908, at one catch 11 such eggs were taken and 

 measured in 3 diameters. They ran in milHmeters, 17 by 18 by 20, 

 18 by 19 by 20, 18 by 19 by 21, 18 by 20 by 21, 19 by 20 by 21, 21 by 

 21 by 22, 22 by 22 by 22, 22 by 22 by 23 (two), 22 by 22 by 25, 23 by 



