Page:Proceedings of the Royal Society of London Vol 60.djvu/292

266 the stomach and tbe incompletely developed swim-bladder, which is as yet free from contained gas, are present both in hrevirostris and in the elver of Anguilla vulgaris. The pronephros is in active function as in the other Leptocephali. The M alpighian glomerules of the kidney (mesonephros) are lobed as in the eel, and their num ber corresponds w ith th at observed in the Helm ichthys stage, of which I will speak fu rth er on. The genital gland, not yet sexually differentiated, is almost identical with th at of the same stage. In short, it may be said th a t the whole organisation of Leptocephalus hrevirostris corresponds w ith the organisation of the Common Eel, if we make allowance for those changes, which are observed in the m atam orphosis of the other species of Mursenoids, such as reduction of the pancreas and of the liver, disappearance of the proto-skeleton, com plication of the musculature, increase in size of the cerebellum, loss of the larval teeth, development of the definitive teeth, &c.

From the description of these Leptocephali I must pass on, briefly, to speak of the stages nearer to the condition of the elver. I am, however, obliged to leave a break in the series, which, however little its significance, yet certainly w ill make some impression on the minds of those who do not realise with what caution I have formed my conclusions. I must confess that since I have learnt how difficult it is to procure an entire series of the development of a Mureenoid, 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 must 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-larvaa which I happened to m eet w ith at the end of the year 1892. They were really transitional stages between Leptocephalus hrevirostris and th at stage which I shall describe fu rth er on. I published this fact in a prelim inary note in the month of May, 1893. They were transparent with almost colourless blood, w ithout any trace of pigmentation except at the eyes, and had lost all the larval teeth, w hilst they possessed already very few and very m inute 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 hrevirostris on the way to transform ation into Anguilla vulgaris. As a m atter of history they actually did transform them ­ selves in my aquarium w ith the usual diminution in th eir dimensions, and subsequently proceeded to increase in bulk. The metamorphosis took place as usual without the animal taking in any