2(i6 Prof. G. B. Grassi. The Reproduction and 



the stomach and the incompletely developed swim-bladder, which is 

 as yet free from contained gas, are present both in Leptocephalus 

 brevirostris and in the elver of Anguilla vulgaris. The pronephros is 

 in active function as in the other Leptocephali. The Malpighian 

 glomerules of the kidney (mesonephros) are lobed as in the eel, and 

 their number corresponds with that observed in the Helmichthys 

 stage, of which I will speak further on. The genital gland, not yet 

 sexually differentiated, is almost identical with that of the same 

 stage. In short, it may be said that the whole organisation of 

 Leptocephalus brevirostris corresponds with the organisation of the 

 Common Eel, if we make allowance for those changes, which are 

 observed in the matamorphosis of the other species of Mureenoids, 

 such as reduction of the pancreas and of the liver, disappearance of 

 the proto-skeleton, complication of the musculature, increase in size 

 of the cerebellum, loss of the larval teeth, development of the defini- 

 tive teeth, &c. 



From the description of these Leptocephali I must pass on, briefly, 

 to speak of the stages nearer to the condition ol the elver. I am, 

 however, obliged to leave a break in the series, which, however little 

 its significance, yet certainly will make some impression on the minds 

 of those who do not realise with what caution I have formed my con- 

 clusions. I must confess that since I have learnt how difficult it is 

 to procure an entire series of the development of a Mura3noid, I 

 am more astonished at being able to recognise a single stage in the- 

 development of a given species than at not finding the whole series. 

 I in nst point out that the break in my series of the development of 

 Anguilla vulgaris would have been much smaller if I could have 

 persuaded myself to kill and preserve one of the hemi-larvae which I 

 happened to meet with at the end of the year 1892. They were 

 really transitional stages between Leptocephalus brevirostris and that 

 stage which I shall describe further on. I published this fact in a 

 preliminary note in the month of May, 1893. They were transparent 

 with almost colourless blood, without any trace of pigmentation, 

 except at the eyes, and had lost all the larval teeth, whilst they 

 possessed already very few and very minute teeth of the definitive 

 series. The body was thickened, and already showed the cylindrical 

 form. They measured little less than 8 cm. In short, they were 

 Leptocephalus brevirostris on the way to transformation into Anguilla 

 vulgaris. As a matter of history they actually did transform them- 

 selves in my aquarium with the usual diminution in their dimen- 

 sions, and subsequently proceeded to increase in bulk.* The meta- 

 morphosis took place as usual without the animal taking in any 



* The fact that I actually hare obtained in an aquarium the transformation of 

 L. brevirostris into Anguilla vulgaris is of prime importance. The time occupied 

 was one month. 



