494 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



detect in the fish's mouth any special mechanism by which drops of 

 water could be formed and expelled. It is, of course, obvious that 

 that there must be some peculiar adaptation or apparatus in Toxotes 

 to account for its extraordinary accomplishment. By carefully watch- 

 ing the fish at close range on many occasions in Thailand, the writer 

 formed an opinion of the probable propelling mechanism, and subse- 

 quently verified that opinion by holding the fish in a basin or bucket 

 of water in the position regularly assumed when shooting and making 

 them perform almost at will. This he accomplished by the quick, 

 forceful compression of the gill covers with his fingers, and by so do- 

 ing he was able to cause a fairly satisfactory imitation of the normal 

 shooting act, and had no difficulty in propelling drops of water for 

 distances up to 3 feet. 



This compression of the gill covers would in itself not account for 

 the escape from the mouth of water in the form of individual drops of 

 uniform size, and it is to the peculiar shape and structure of the 

 mouth parts that we must look for the additional factors necessary for 

 the complete and perfect performance. 



The mouth cavity of Toxotes is long but its diameter is much re- 

 stricted by the projecting sides of the roof and by the large tongue, 

 which when raised may completely close the passage to the pharynx. 

 The anterior part of the tongue is free from the floor of the mouth, 

 and its rounded tip is of paperlike thinness and fits snugly against the 

 palate ; posteriorly the tongue is thick, bears minute teeth, and has a 

 conspicuous fleshy prominence. Extending along the median line of 

 the roof of the mouth, from a point just behind the band of vomerine 

 teeth to the pharynx, is a deep groove which, when the tongue is ap- 

 plied to the roof of the mouth, becomes converted into a tube. This 

 groove-tube, which in a fish 7 inches long is less than a sixteenth of an 

 inch in diameter, not previously described or referred to in ichthy- 

 ological writings, may readily be seen when the tongue is depressed. 

 That it should have been so long overlooked is something of a mystery 

 when one recalls the vain efforts made by Oriental ichthyologists to 

 discover any special adaptation for drop shooting. 



It is not difficult to discern the manner in which the shooting fish 

 operates. With its tongue closely pressed against the palate, the 

 sudden compression of the gill covers will force water from the phar- 

 ynx into the palatine canal, and with the tip of the tongue acting as a 

 valve, the flow of water under pressure from the anterior end of the 

 tube is regulated. With the jaws partly separated and the mouth 

 reaching or projecting slightly above the surface, the water is ejected 

 with a force and for a distance that depend on the pressure. It is 

 easy to understand how, with the pharyngeal cavity serving both as a 

 reservoir for water ammunition and a compression chamber, it is 



