172 CARNEGIE INSTITUTION OF WASHINGTON. 



Hcemulon album, Anisotremus surinamensis, Chromis insolatus, and Lepisoma 

 nuchipinne. 



It was observed that of the 14 species enumerated, 9 are changeable in colora- 

 tion. The changes of M. dimidiata, S. chrysopterum, and L. nuchipinne are 

 of a particularly striking character, and those of the three species of Hoemulon 

 and Aulostomus only less so. Decapterus is also changeable. Upon the 

 whole it is clear that the color changes here mentioned must be looked upon 

 as adaptations to environments changing as the location of the fishes changes. 

 Among species previously well known at Tortugas, adaptive color changes 

 were observed in Hcemulon sciurus, Scarus coeruleus, S. croicensis, S. pundu- 

 latus, and Pseudoscarus guacamaia. 



Observations of the most varied sort were made upon other species. 



The young red parrot-fish (Sparisoma ahildgaardi) 3 inches in length some- 

 times shows a pattern of longitudinal stripes, such as characterizes many 

 labrids and scarids permanently in their adult coloration, or is displayed as 

 one of their alternative color phases, or, it may be, appears only in their 

 juvenile coloration. This particular phase has not been observed in mature 

 specimens of this species. 



A fish of the comparatively rare type which fishermen (probably correctly) 

 consider to be the result of a cross between the yellow-tail {Ocyurus chrysurus) 

 and the gray snapper {Neommnis griseus) was repeatedly seen with normal 

 yellow-tails at their schooling-grounds. These fishes, no doubt, feed in quite 

 other places at night, indicating that fishes possess a marked homing instinct 

 and sense of location or direction. It has been noted in previous reports that 

 the Hsemulidse as a whole belong to the group of fishes that feed by night and 

 spend the day more or less inactively about selected schooling-places. Brachy- 

 genys chrysargyreus and Bathystoma rimator apparently constitute no real ex- 

 ception to this rule, but in their young stages at least they feed freely by day 

 upon plankton. A single 2-inch specimen of Bathystoma, one of a number 

 feeding actively toward the tideward side of corals about which they were 

 gathered, contained about 1,000 copepods. 



Small specimens of Mionurus puncticulatus are sometimes found in dead 

 tests of echinoids or in Stromhus shells. But in a collection of 23 living Pinna, 

 taken at random except for the fact that large individuals were chosen, 8 

 were found, most of which were larger than any others observed at Tortugas. 

 It therefore appears that this species may almost be said to live symbiotically 

 with the mollusk. 



Ichthyologists recognize many varieties of Hypopledrus unicolor. Some 

 have considered these distinct species; others, mere color variations. To one 

 accustomed to the rapid changes in coloration which other species undergo, 

 these various forms appear surprisingly constant in appearance. But two 

 at least are only alternative color phases of one species, for a single individual 

 has been observed in nature to display alternately the coloration of H. uni- 

 color and H. unicolor nigricans. Another individual of the variety last named 

 also showed in the aquarium marked ability to change its shade, without, 

 however, modifying its pattern. 



The body of Petrometopon cruentatus is marked with numerous dark-brown 

 spots. On the head these are smaller dorsally and larger on the side and 



