Metamorphosis of the Common Eel. 265 



further conclude that seven other vertebras are developed at the 

 caudal extremity, as indicated by the number of vertebral arches and 

 the spinal ganglia in that region. We count, therefore, in all 115 

 vertebrae, and this is the number which can be easily seen in many 

 specimens of Anguilla vulgaris. 



Here I must particularly insist that I have .ascertained in an 

 absolute manner that during the metamorphosis of the Mureenoids, 

 the number neither of the myomeres nor of the vertebral arches, nor 

 of the spinal ganglia is subjected to any change. The hypurals of 

 Leptocephalus brevirostris are precisely 'the same as in the elver of 

 Anguilla vulgaris. The last hypural which is fused with the urostyle 

 may present itself as a single piece, or may be more or less cleft. 

 These are variations which are met with also in the elver. Just as 

 in the elver, the last hypural but one is always extensively cleft, or, 

 if the expression is preferred, doubled. To the last hypural corre- 

 spond five rays, whilst four correspond to the last but one, and one to 

 the last but two, the whole structure being identical with that found 

 in the elvers of Anguilla vulgaris. Of these ten rays, the eighth, 

 seventh, and sixth are bifid, both in Leptocephalus brevirostris and in 

 the elvers of Anguilla vulgaris. In the pectoral fin of Leptocephalus 

 brevirostris the definitive rays can be observed, and these are of the 

 same number as in the elvers of Anguilla vulgaris. Leptocephalus 

 brevirostris is transparent, and has colourless blood. The red cor- 

 puscles are wanting, but there are present so-called " blood-plates " 

 (" Blutplattchen " in German) similar to those of the inferior 

 vertebrates. The bile is also colourless. This fact is observed in all 

 the other Leptocephali. Leptocephalus brevirostris is, however, the 

 only one which is free from all pigmentation. Correspondingly, the 

 Common Eel is the only species of Muraenoid which at the close of 

 metamorphosis is devoid of all trace of larval pigmentation. It was 

 this observation which first led us to the discovery of the relations 

 between Leptocephalus brevirostris and Anguilla vulgaris. 



In making transverse sections of Leptocephalus brevirostris, I found 

 other characters which confirm the relation between it and the Com- 

 mon Eel ; for instance, the branchiostegal rays are ten to eleven in 

 number, as is also observed in the elvers of Anguilla vulgaris. In the 

 Common Eel the well-known lateral branch of the fifth pair of the 

 cranial nerves exists. It is also found in Leptocephalus brevirostris. 

 This lateral branch could not be found by Dr. Calandruccio in the 

 other common Murasnoids of Sicily, and is wanting also in the other 

 Leptocephali. 



The mucous-canal-system (sensory canals) in the head are already 

 developed, partially, in Leptocephalus brevirostris, and are incom- 

 pletely developed in the elver. As in the elver, so in Leptocephalus 

 brevirostris, the pyloric cceca are wanting. The blind extremity of 



