30 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



development of the young of these fresh-water flatfishes, which are 

 worthy of special study. 



Everywhere observable and constituting a salient feature of the fish 

 life of streams, lakes, swamps, and marshes are the serpenthead fishes, 

 the Ophicephalidae, which are represented by eight species. 



The Anabantidae are largely represented in Thailand. In some of 

 the local genera, six in number, the gills appear inadequate to maintain 

 the necessary respiratory functions, and the fishes are dependent on 

 atmospheric oxygen, which they are able to appropriate by means of 

 acc^essory breathing organs developed from the branchial arches and 

 occupying special cavities in the head. These fishes are monogamous 

 and blow masses of glutinous bubbles for the reception of their eggs. 

 Several members of the family are among the choicest of Oriental food 

 fishes, and several are among the most attractive of aquarium fishes. 



Conspicuous fishes on flats and river banks exposed at low tide are 

 the periophthalmid gobies, whose movements and antics out of water 

 afford never-ending amusement to human observers. Inasmuch as 

 these fishes are sometimes seen resting with their caudal fin and 

 posterior part of their body still in the water and with the fore parts 

 and head propped up by their pelvic fins, some persons have asserted 

 that the submerged caudal fin is employed as a respiratory organ. 

 This statement does not rest on adequate observation or on sound phys- 

 iological grounds. The brief aerial excursions of these fishes on the 

 mud flats do not necessitate the invoking of a special caudal breathing 

 apparatus. The gills, in their closely shut-in cavities, retain sufficient 

 moisture to sustain the respiratory processes until the fish plunge into 

 their burrows or into open water. On emerging from the water they 

 proceed cautiously and may at first expose only their eyes or the 

 anterior part of the body until the absence of danger is assured, but 

 more frequently than otherwise the observational point is wholly out 

 of the water, on a mud flat, on a shell or stone, on a stick, or on the 

 root of a mangrove tree. This subject has been dealt with by Dr. 

 Sunder Lai Hora, of the Zoological Survey of India, who has had 

 ample opportunity for observation and abundant material for experi- 

 mentation. His conclusion is that the caudal fin in these fishes does 

 not and cannot serve as a respiratory organ. Scarcely less noteworthy 

 than the aerial movements is the degree to which aerial vision has 

 developed, enabling the fish to detect, pursue, and capture small food 

 objects on the tide flats. 



SOME PECULIARITIES OF STRUCTURE AND HABITS AMONG THE 

 FRESH-WATER FISHES 



In a preceding section reference was made to the development in 

 two families of catfishes, the Clariidae and the Heteropneustidae, and 

 in the Anabantidae of respiratory apparatus accessory to the gills. In 



