or THE LARVAL POLTPTEEUS. 317 



in this larval Crossopteryj2:ian, attempting such interpretation as they seem to warrant, 

 in view of the absence of knowledge of the early stages in its development. 



II. — Material. 



The external features of the larva of Polypterus, which forms the subject of this 

 paper, I have described in a former paper ^. I have had at my disposal only a single 

 specimen, measuring 30 mm., obtained during a collecting-trip to the Gambia in 1900^. 

 In the present paper I have given an account of the structure of the cartilaginous 

 skeleton in this larva, and somewhat of its subsequent development as studied in a 

 number of specimens measuring from 9 cm. upwards. I have also given an account 

 of the genital and excretory system of organs in this small larva, the subsequent 

 development of which I have already described in a previous paper ^. 



It will be seen that between the stage of this small larva (30 mm. in length) 

 and the next stage at my disposal (namely, specimens 9 cm. in length) there is a 

 considerable gap. As regards the study of the development of the skeleton, this is 

 of no importance, as the intervening stages are easily interpreted. As regards the 

 development of the genital ducts, however, an intermediate stage, between that here 

 described and that of the 9 cm. larva already described, is much to be desired. Of the 

 developmental stages of Polypterus preceding that here described hitherto nothing 

 has been observed. 



It may be said of this larva that it exhibits the condition of the last of the series of 

 changes which is undergone by Polypterus in its development from the egg before it 

 assumes the external appearances of the adult form. The term " larva " has frequently 

 been employed for young Polypteri of all sizes which retain the external larval gill ; 

 but as this gill is retained frequently by adult specimens of some species of Polypterus, 

 it is in no way justifiable to term such specimens as happen to possess this organ 

 " larvae," irrespective of their being in a larval condition otherwise. 



I have laid some stress upon this, as an account of the excretory system of a larval 

 Calamoiclithys has been published, in which I am sure that the author has been 

 influenced in his description by the supposition that the specimen was in a larval 

 condition, though measuring 12 cm. in length. But to this I shall return later. 



Methods, 



The larva, which had been preserved in 5 per cent, formalin, was cut into transverse 

 sections, of which the anterior half were 10 fx in thickness, while the posterior half 

 were 7 ^ thick. They were doubly stained with heematoxyline and eosine. All the 



^ Trans. Zool. Soc. London, vol. xvi. p. 118. 



' In the account of the external features, this larva was said to be of Polypterus lapradii. It has recently 

 been shown by Mr. Boulenger that the larva is that of P. senegalus and not that of P. lapradii. 

 ' Trans. Zool. Soc. London, vol. sv. p. 323. 



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