PARALLEL EVOLUTION IN THE FISH AND TADPOLES 

 OF MOUNTAIN TORRENTS. 



By N. Annandale, D.Sc, F.A.S.B., Director, and Sunder 



Lal Hora, M.Sc, Assistant Superintendent, Zoological 



Survey of India. 



The structural modifications of the fish and of the Batra- 

 chian larvae that inhabit the small mountain torrents of the 

 Oriental Region afford a remarkable instance of parallel evolu- 

 tion on a comprehensive scale. The phenomena they exhibit may 

 indeed, be called communal convergence. One of us ' has quite 

 recently discussed these modifications in the fish, while the other 1 

 has from time to time published observations on the external 

 features of the tadpoles. We propose in the present paper to give 

 a short general survey of the facts and to discuss a specific instance 

 in anatomical detail. 



Speaking generally, modifications in the tadpoles Of moun- 

 tain torrents chiefly consist either in the formation of floats for 

 floating away lightly on the surface of the flood, as in some spe- 

 cies of Megalophrys, or in that of " suckers " for clinging to fixed 

 objects. 



These structures in the tadpoles seem to have been evolved 

 independently of any high degree of specialization in the adult 

 frog or toad, 8 just as the larva of an insect may be highly 

 modified in correlation with a peculiar mode of life, while the 

 adult remains of an unspecialized type. Identical structural 

 resemblances in the tadpoles mean that a true genetic affinity 

 exists, but similar structures are frequently evolved independ- 

 ently for the same function but along different lines, for ex- 

 ample the oral float on the mouth of the larvae of certain species 

 of Megalophrys * and that on the mouth of Microhyla achalina* 

 or the powerful oral sucker of the tadpole of Helophryne natal- 

 crisis 9 and that of Bufo penangensis. 1 In the floats of the two 

 former tadpoles there is a general similarity in form and function, 

 but in the Megalophrys the internal surface of the float bears 

 rows of peculiar horny tooth-like processes and these are replaced 



1 Horn, Pec. Ind. if us. XXIV, pp. 31-36 (1922). 



2 Annandale, Pec. Ind. Mus. VIII, p. 29(1912} ; ibid. XV, p. 17 (1918) 

 Proc. As. Soc. Bengal (n. s.) XIII, p. clxxxvi (1917). 



B Boulenger, Pec. Ind. Mus. XV, p. 65 (1918). 



% Hora. Journ. As. Soc. Bengal (.1922). 



6 Smith, Journ. Nat. Hist. Soc. Siam II, p. 37, figs. A|-A t (1916). 

 * Hewitt, Ann. Natal Mus. II, p. 477, p!. xxxix, figs. 5, 6, 7 (1913). 



7 Flower, Proc. Zool. Soc. London, p. 908, pi. lx. figs, 3, 3a (1899). 



