40 EEPRODUCTION AND DEVELOPMENT OF THE CONGEE. 



larger specimens were tlie younger, and that fhe metamorpliosis into 

 Balanoglossus was accompanied by a considerable reduction in size. 

 Such a reduction in size is, in fact, a very common feature in meta- 

 morphosis. I have found that the larval symmetrical flounder is 

 considerably longer than the metamorphosed asymmetrical fish. It 

 seems to me that the theory of an abnormal continued growth of 

 larvae, with arrested development, is at present entirely unsupported 

 by evidence, and in any particular case can only be proved by the 

 actual demonstration of the normal development and of the abnormal, 

 togetlier with proof that they are independent of one another. 



However, to return to the case of the conger, I find that the 

 French ichthyologist. Dr. Emile Moreau, in his Poissons de la France, 

 tome iii, p. 568, claims to have satisfied himself by anatomical 

 investigation that the Leptocephalus Morrisii is the young Conger 

 vulgaris. Moreau does not refer to any publication of his anatomical 

 researches, or even mention that he ever published his conclusion in 

 any other place than that I refer to, but he states that M. Dareste 

 appropriated his results in a Note sur le Leptocephale de Spallanzani 

 in the Comptes Rendus, tome Ixxvi, 1873, p. 1304. Moreau asserts 

 that Dareste examined his preparations of Leptocephalus and conger, 

 but made no dissections himself. 



If the evidence went no further than this, the conclusion that 

 Leptocephalus Morrisii was the larval conger would rest merely on 

 anatomical and zoological resemblances between the two forms. If 

 it had been discovered that the Leptocephalus was developed from 

 the eggs of the conger, proof would still be wanting that the former 

 was a normal stage in the development of the latter, and Giinther^s 

 theory of the abnormal growth of the larva would remain uncon- 

 tradicted by observed facts. But the metamorphosis of a Lepto- 

 cephalus Morrisii into a normal conger has actually been once ob- 

 served. This observation was made by the distinguished French 

 zoologist, Yves Delage, and is described briefly in the Comptes 

 Rendus, tome ciii, 1886, p. 698, The particulars are as follows : — 

 Two specimens of Leptocephalus were captured on February 7th, 

 1886, by the keeper of the Laboratory of Roscofi-', in Normandy. 

 One of them was damaged, and was preserved in alcohol The 

 other was uninjured, and was kept alive in a tank of sea water. 

 Unfortunately Delage, strange to say, omits to give the dimen- 

 sions of these two specimens. On April 18th the living Lepto- 

 cephalus was still ribbon-shaped and absolutely transparent^ all its 

 blood was colourless, and the air-bladder was not visible. On 

 May 1st the skin began to get a little dark, the air-bladder appeared 

 in the form of a silvery streak, the gills began to show a pink 

 colonisation. On Mav 9th the fish was examined alive under the 



