DEPARTMENT OF MARINE BIOLOGY. 205 



are very abundant in large, deep holes in the reef flats. Two fishes and 

 two shrimps have been seen living together, but usually only one of each ap- 

 pears to share the burrow. 



Species of Gnathypops and Opisthognathus dig and occupy holes in a sandy 

 or stony bottom, and are able to line vertical shafts and prevent their collapse. 

 They have been seen working in the bottom of funnel-shaped depressions, 

 whether excavated by themselves or not is uncertain. About the mouth of a 

 shallow pit in the bottom of such a hole they arrange a circle of stone or bits of 

 shell not too large to be carried in their mouths, and support these externally 

 by banked sand brought up from the burrow or carried in from outside. From 

 time to time additional stones are laid in place, additional sand is brought, 

 and their building is carried up until it reaches the level of the surrounding 

 bottom, or even rises above it. The plumbness and fit of the shaft are assured 

 by the fact that when the fish returns with a coral fragment in its mouth it 

 goes down into its hole tail first and lays its burden accurately in position, 

 or moves it repeatedly until it is fitly adjusted. Opisthognathus macrognathum 

 (Poey) may build in this way a retreat a foot or more in depth, with a shaft 

 an inch or more in diameter, and with a terminal chamber of a pint capacity. 

 The fish usually stands in its burrow with its head scarcely rising above the 

 general surface, and when it retires it may draw in and block the opening 

 with a piece of coral relatively huge in proportion to its own size and weight. 



Thalassoma nitidum (Gunther), which the writer has perhaps incorrectly 

 considered the young of T. hifasciatus (Bloch), is apparently an active gleaner 

 of ectoparasites from the bodies of other fishes. It may commonly be seen 

 pecking at their sides and fins. Carangids, tangs, and others come singly 

 or in groups again and again to the point where the Thalassoma is temporarily 

 located, one might almost say with the specific intention of submitting them- 

 selves to its inspection. A chub, K. sectatrix (Linnaeus), has been observed 

 to drive away others repeatedly to a distance of 20 feet or more and to return 

 promptly and permit the interrupted grooming to be resumed. 



It is interesting to discover a blenny, apparently an undescribed species 

 very like T. nitidum in color, very rare, found sometimes in its company. 

 The relation between the two species seems comparable to that between 

 Batesian mimics and their models in the case of Lepidoptera. It will be 

 interesting to learn whether T. nitidum, on account of its beneficent ministra- 

 tions, or for other reasons, enjoys immunity from attack which the unnamed 

 species might share on account of its similarity in appearance. 



Epinephelus morio (C. and V.), E. striatus (Bloch) Kyphosus sedtarix 

 (Linnaeus), and several species of Eupomacentrus show more or less distinc- 

 tive color-phases when in pursuit of other individuals of their respective species 

 which may have entered their private preserves, or otherwise provoked attack. 

 These changes in color are examples of those to which Mr. Charles H. Town- 

 send has called attention as a result of his observations on fishes in the New 

 York aquarium. In some degree at least they appear to differ in cause and 

 significance from other color-changes occurring in these and other species. 

 For it remains true in general that the evidence indicates that the chief func- 

 tion of fixed or changeable coloration in tropical reef fishes is to render them 

 inconspicuous under the conditions in which they live. 



