118 
SPOLIA ZEYLANICA. 
There are several other points with regard to which comparisons 
with other forms may be both instructive and interesting. The 
simple ventral flexure of the embryo of Ophiocephalus , the absence 
of retinal pigment within the egg, and the formation of the pectoral 
fins after hatching, are facts to be noted as contrasting with what 
occurs in the development of many other Teleostean fishes. The 
later appearance of the ventral fins is the rule amongst bony fishes.* 
In the two Dipnoan fishes, Lepidosiren and Protopterus, the paired 
limbs arise simultaneously ; in the former thirteen days after hatch¬ 
ing ; f in the latter, according to Budgett, the rudiments of the limbs 
begin to show about the third day after hatching, and by the tenth 
day after hatching the larva is provided with well-developed limbs. J 
On the other hand, in the Australian Dipnoan genus Ceratodus, 
according to Semon’s observations,§ the ventral fins appear about a 
month later than the fore-limbs, approximating in this respect to 
what I have described above for Ophiocephalus. In this connection 
it is interesting to note that in the genus Channa , which also belongs 
to the Ophioceplialidse and occurs in Ceylon, the ventral fins fail to 
put in an appearance throughout life. 
As described above, the development of the definitive caudal rays 
of Ophiocephalus is marked by a succession of phases : firstly, the 
proliferation of primordial or formative tissue below the posterior 
end of the notochord ; then the formation of a capillary plexus; the 
development of basal cartilages and the fasciculation of the primary 
striations ; lastly, the appearance of the basal prongs. The actual 
rays thus arise peripherally or centripetally ; and this relation 
appears to be more pronounced in the case of the anal rays (Eig. 14). 
An analogous peripheral origin of fin-rays has been described by J. 
Schmidt in the pelagic larvse of the marine salmonoid fish, Argentina 
situs , where at a stage of 28-32 mm. in length, the primordia of the 
dorsal and anal interspinous rays appear nearly half-way between 
the contour of the body and the outer border of the embryonic fin, 
without direct connection with the body. At a length of 39 mm. the 
fin-rudiments touch the margin of the body.|| The general ontogeny 
of the median fins of Ophiocephalus resembles that described and 
figured by Assheton for Heterotis niloticus .^[ 
The rhythmical darts to the surface for the gulping of air by the 
28-day larvse of Ophiocephalus is paralleled by the larvse of Gym- 
narchus , although the latter are burdened by an enormous pendent or 
F. M. Balfour. Comparative Embryology, 2nd edit., 1885, Vol. II., p. 80. 
f J. G-. Kerr. Development of Lepidosiren paradoxa. Phil. Trans. R. Soc., 
London, Vol. 192, 1900, p. 316. 
$ J. 8. Budgett. Op. cit. PI. VIII., figs. 12-13, p. 127. 
§ R. Semon. Forschungsreise ; quoted from Kerr, loc. cit. 
|| J. Schmidt. Development of the Argentines. Medd. fra Komm. Fiskeri 
II., No. 4, Copenhagen, 1906. 
R. Assheton. Teleostean Larvse from the Gambia River. Budgett 
Memorial Vol., Cambridge, 1907, p. 439. 
