igi6.] Fauna of the Chilka Lake : Larval Fish. 391 



the heterocercal and homocercal type — a rather nearer approach to the latter. The 

 caudal fin-rays are quite distinct. 



The gradual growth of the myotomes has increased the opacity of the body. 

 The chromatophores of the last stage have all disappeared, except of course those of 

 the gas-bladder. In their place we find a paired ventral row of chromatophores, 

 which probably become attached together and form a continuous streak between the 

 anus and the caudal fin. A middle paired row (one on either side of the body) consisting 

 of about 24 chromatophores, occurs on the sides of the body and in a lateral view 

 seems to lie over the notochord. A dorsal paired row lies on the dorsal surface of the 

 body. Each row consists of 16 distinct anteriorly situated chromatophores, and a 

 continuous streak posteriorly consisting of about 9 chromatophores. Pigment spots 

 also make their appearance in the upper jaw. Large irregular pigment bodies are to be 

 seen on the dorsal and lateral sides of the head. They are irregular in their distribu- 

 tion (not shown in the figure). Ventrally in the anterior region of the trunk close 

 behind the head, a line of small black pigment spots make their appearance. The 

 dorsal and ventral fin-folds still exist, though in a much more modified form. The 

 dorsal and anal fins are developed, but their skeletal structures are not yet 

 visible. 



Stage VI (pi. xviii, fig. 5). There is not much difference between this stage and 

 the previous one. The snout in particular shows very little increase, while the general 

 increase in length is 75 mm. The bony framework of the skull is developing fast ai d 

 the head region has become quite opaque except on the ventro-lateral edge, where 

 the branchiae are just visible through the operculum. The gas-bladder becomes more 

 densely pigmented, All the 3 paired rows of pigments described in the previous 

 stage are present. The pigments in the head region are repeated again as in the 

 previous stage, except that now the beak also acquires pigments. 



The tail acquires true homocercy. The caudal fin-rays are well developed, and 

 faint traces of segmentation are visible in it. The myotomes have considerably grown 

 in thickness and nearly completely hide the notochord from view. There are about 

 45 myotomes of which 40 are quite distinct. The dorsal and anal fins are fairly well 

 developed and their skeletal structures are also visible. Very faint traces of them 

 were really found in the previous stage. A careful examination under the high power 

 of the microscope reveals the presence of pterygiophores (Parker) or radial elements 

 (Bridge). Corresponding to each fin-ray there is a baseost and an axonost (Cope), the 

 former lying between the heads of two adjacent axonosts as a small round body. 

 The ventral fin-fold still persists, though the dorsal fin-fold disappears. Another 

 striking feature is the appearance of the pectoral fin close behind the operculum. 



Stage VII. The general pigmentation of the body is the same as in the previous 

 stage. The pigments in both the upper and lower jaws and the head are better 

 developed than in stage VI. The fins are pigmented. 



Stages VIII, IX, X, XI, and XII. These stages are marked by the gradual 

 growth of the body, beak, and gas-bladder. The pigmentation is practically the same 

 as in stage VII. A gradual growth of the gills, the bones of the skull, and the 



