Page:Popular Science Monthly Volume 11.djvu/199

Rh in the existence of two tails, an upper and a lower. These are shown in Fig. 8, B.

The formation of these two tails, and their significance, will be considered further on; for the present, we are concerned with their Structure, their relative position, and their uses. The lower tail was



 A, from a specimen twenty-two millimetres or seven-eighths inch long, enlarged four diameters. The ventral fin (Ve) is just appearing. The median fin is being absorbed between the fourspots referred to in Fig. 9. The lip of the tail is inclined upward, and the infra-caudal lobe is larger. In B the primordial fin has almost disappeared; the dorsal (D) and the anal (A) fins are quite large. The infra-caudal lobe is nearly as long as the tip of the original tail, which has been reduced to a slender vibratile filament. This specimen is forty-four millimetres or one and three-fourths inch long, and the tail is enlarged two diameters. C shows the tail of a specimen three hundred millimetres or nearly twelve inches long, of natural size. The filament is still further reduced, and the rays of the infra-caudal lobe form the end of the tail In D the fail is that of an adult, one-half natural diameter. The filament, the original end of the body, has wholly disappeared, and the infra-caudal lobe forms the tail. But dissection shows the spinal axis extending along the dorsal border to a point corresponding with the previous attachment of the filament. (Further description and discussion of these changes, with references to authors, may be found in a paper by the author, entitled "Notes on the North American Ganoids." "Proceedings of the American Association for the Advancement of Science," 1875, pp. 151-193.

evidently the caudal fin. It had several rays, and a rounded hinder border. But it was smaller in proportion than in the adult gar, and the middle rays were directed obliquely downward, instead of horizontally backward.

The upper tail is best described as a single fleshy filament,