384 Memoirs of the Indian Museum. [Vol. V, 



out under the high power of the microscope. The apertures in the last row (distally) 

 do not keep an exactly oval shape, but are generally slightly curved or bent and 

 much more elongated than broad. 



The egg shown in pi. xvii, fig. 1 was the smallest of the lot I came across and 

 measures - 5 mm. in length. It is in one of the early stages of development. 

 Numerous small globules, very likely oil globules, may be seen in the yolk-mass. The 

 egg-membrane is more or less closely attached to the developing egg. The exam- 

 ination of the contents of the egg seems to show, however, that it is really a 

 degenerate egg. 



The egg in pi. xvii, fig. 2 measures i"6 mm. in length. Intermediate stages 

 between figures 1 and 2 could not be found. At this stage the embryo is fairly well 

 developed. In a lateral view the eye, ear and heart may be seen to have begun to 

 develop. The eye has not yet acquired pigments and is consequently colourless. The 

 ear is a simple pit-like depression. The heart is represented by a very minute sac-like 

 dilatation. The yolk-mass lies in a yolk-sac on the ventral surface of the body. 

 Immediately above the yolk-mass we see the beginning of the notochord which 

 gradually tapers towards the tail end, though it has not yet reached its extremity. 

 On the dorsal surface of the embryo from the anterior end to about the middle of the 

 body a thickening like that of the neural plate is observable. It marks the beginning 

 of the development of the nervous system. A continuous fin-fold all over the body, 

 except for a small portion of the head-end of the embryo, forms one of the most 

 characteristic features of the embryo at this stage. 



Plate xvii, fig. 3 shows an empty egg-membrane from which the embryo has been 

 extruded. The wavy line at the upper end marks the point of rupture daring extrusion. 



The specimen in pi. xvii, fig. 4 measures 2 mm. At this stage we find the 

 nervous system fairly well developed. The notochord reaches the extremity of the 

 tail and is slightly curved upwards (heterocercal) , and the caudal fin-fold acquires a 

 corresponding shape. The epichordal lobe becomes reduced in size and the hypo- 

 chordal lobe becomes comparatively enlarged. The continuity of the fin-fold is more 

 or less broken near the middle of the body by its extreme narrowness, and we get 

 anteriorly a dorsal fin-fold, posteriorly a caudal fin-fold, and ventrally a pre-anal fin- 

 fold. The transition from fig. 2 to fig. 5 is rather abrupt. A truly heterocercal stage 

 is not visible and we apparently get a homocercal (fig. 7) from a diphycercal (fig. 2) 

 type. Fig. 5, however, approaches the heterocercal stage to some extent. Black 

 stellate chromatophores lie in streaks both above and below the notochord , but do 

 not reach the caudal extremity. The anus lies near the middle of the body, but the 

 anterior portion of the alimentary canal is either undeveloped or indistinct. The 

 heart acquires a coiled shape. 



Plate xvii, fig. 6 shows a slightly more advanced stage. It has a curved tail, 

 which is of course not a characteristic feature of this stage, for many specimens of 

 earlier stages possess coiled or curved tails. This stage marks the development of 

 pectoral fins and of another stucture— probably the gas-bladder which lies just in front 

 of the yolk-mass, 



