(From photographs by the author.)

1. Raphiodon vulpinus Spix.

2. Astyanax bimaculatus brevoortii Gill.

3. Serrasalmo humeralis Cuv. & Val.

4. Henochilus wheatlandi Garman.

5. Acestrorhynchus falcatus Bloch.

6. Hoplerythrinus unitæniatus Spix. (Head resembles that of Amia.)

7. Leporinus conirostris Steindachner.

8. Prochilodus scrofa Steindachner.

9. Aphiocharax dentatus Eigenmann & Kennedy.

SOME SIMILARITIES IN THE CHARACINS.
(All figures after Steindachner.)

1. Luciocharax insculptus, a Garpike-like Characin.

2. Salminus affinis, a Salinon-like Characin.

3. Prochilodus longirostris, a Sucker-like Characin.

4. Chalcinus magdalenæ, a fresh water Herring-like Characin.

5. Gasteropelecus maculatus, a flying Characin.

6. Myleus knerii, a Pompano-like Characin.

7. Nannostomus unifasciatus, a Cyprinodont-like Characin.

burrow in the sand in the bottom of the river, others fly with wing strokes through the air above the river, and others occupy all possible spaces between. In appearance they parallel our garfish, our pickerel, our top minnows, our pompano, our trout, our minnows, our suckers, our darters, our fresh-water herrings and shad; and besides these there are a variety of shapes and sizes and adaptations not to be found in other fishes. Chief of these is the series ending in a true flying fish, i.e. a fish with wing-like pectorals, large muscles to move them, and the ability to propel itself with wing strokes along the surface of the water for forty or more feet, and to continue its flight for five or more feet in the air.

C. CAUSES OF ADAPTATIONS. The causes leading to new adaptations may be intrinsic or extrinsic. The theories of Nägeli, Weismann, and, in part, of Darwin and De Vries, are based on intrinsic causes; those of Buffon, Lamarck, Gulick on extrinsic.

D. ORTHOGENESIS. Nägeli, and in a modified form Eimer, Waagen, Osborn, Whitman, and others, have shown that lines of evolution are orthogenic, predetermined in definite directions. According to Nägeli direction is maintained by the make-up of the protoplasm of the individual. According to Weismann direction is given by the process of germinal selection, helped out by personal selection. By Osborn and others it is recognized but not explained.

The Characins offer us the very best imaginable proof, both for orthogenesis and against its universality. The fact that lines of evolution radiate in so many directions in this family is absolutely conclusive proof that there are many possibilities, that evolution to adaptive points may not only take place along one line or parallel lines, but along very many diverging lines. On the other hand, the fact that there are lines with but few breaks leading from the generalized central type to such aberrant forms as the minute sand-burrowing Characins, duplicating our sand darters, or to the death-dealing Serrasalmo, or the flying Gasteropelecus, shows that, a path of adaptive modification once entered upon by these fishes, evolution along that line may take place, even beyond the point of highest advantage. These lines are not parallel and can not therefore have been the result of the inherent make-up of the family.' They have in some way been determined and are being followed to the limit.

E. MUTATIONS. The possibility of divergence in many directions has been experimentally demonstrated by De Vries, who, with others, has claimed that the line of adaptive modification is broken, not bent. Waiving the question of whether the difference between the bend and break is one of kind or degree, permit me again

1 Similar characters like a pair of canines or ctenoid scales have appeared in very diverse genera both in Africa and in South America.