1916.] Fauna of the Chilka Lake : Larval Fish. 387 



yet imperfecta developed. The operculum is fairly well developed and the gills may 

 be easily made out under the microscope. The mouth is armed with sharp pointed 

 teeth. 



Plate xvii, fig. 10 (stage III) measures 15-9 mm. in total length (inclusive of the 

 middle caudal rays). The myotomes are well developed. As far as could be made out 

 under the microscope there are about 42 myotomes on each side of the body. The 

 " concentration " of muscle segments must have taken place in the region of the paired 

 fins, and in the most anterior and posterior regions of the body, but throughout its 

 greater length the correspondence between muscle segments, radial muscles, unjointed 

 fins or spines, and the superficially segmented dorso-lateral and ventro-lateral dorsal 

 and anal fin-folds respectively— as I propose to call them — is very remarkable A 

 reference to figures 9, 10 and 11 will show that on each side of the dorsal and anal fins 

 there is a membranous superficially segmented fin-fold containing towards the distal end 

 a number of black pigment spots or chromatophores. These membranous fin-folds are 

 devoid of spines (fig. ne), and their segmented portions or processes are very short, flat 

 and blunt. The dorsal fin consists of the conical muscle processes at the base, from the 

 apex of which (I could not see any close connection between the two) arise unjointed 

 rays or spines (fig. 11). A muscle segment or myotome corresponds with a radial 

 muscle process, a spine, and a segment of the dorso-lateral membranous fin-fold on each 

 side. This correspondence even in the post-larval stage lends support to the theory 

 of segmentation in vertebrates. Certainly later on during development this arrange- 

 ment undergoes a great deal of modification so essential to keep up the rigidity of the 

 body in order to keep pace with the growingly active movements of the animal. The 

 conical muscle prominences, which in all probability are radial fin muscles, seem to 

 hide from view the corresponding radialia or somactidia, for they are not visible any- 

 where even under the high power of the microscope. These conical prominences are 

 not yet separated from the myotomes from which they are developed. 



A comparison with the Petroscirtes species juv. described by Max Weber in Die 

 Fische der Siboga Expedition, published in Leiden, 1913, will show certain striking 

 differences. Max Weber describes in his specimens the dorso-lateral folds as being 

 provided with elongated spine-like processes, but in my specimens the processes are very 

 short, flat and blunt. Again he shows only one pigment spot (which is comparatively 

 bigger) in each segment of the anal fin close to the base of the spine, but in my 

 specimens a number of comparatively smaller pigment spots lie more or less in a row 

 not at the base of the anal fin, but at the apex of each dorso-lateral and ventro- 

 lateral fin-fold segment. Again he shows the pigments only in the anal fin, but in 

 my specimens they occur both in the dorso-lateral and ventro-lateral fin-folds in the 

 same positions. He also shows a number of smaller spines in the operculum, which 

 are absent from my specimens. These differences provide ample evidence to prove 

 that my specimens belong to a different species to that described by Max Weber. 



The caudal fin is composed of 24 jointed fin-rays. The pectoral and ventral fins 

 are fairly well developed, the former being deeply pigmented towards the distal end. 

 The opercular spine, eyes, and mouth are well developed. A short, blunt and flat 



