THE HISTOLOGY OF THE BLOOD OF LARVA OF LEPIDOSIREN PARADOXA. 437 
mesenchymatous cells, maintained by Lacuxrsse, has been upheld by most of the 
recent workers, especially by Tonxorr, Kotumann, KerpBet, and PIpEr.* 
My observations on the blood of Lepidosiren have not included the first origin of 
the blood and vessels, but have been directed specially on the later phases, for the 
study of which Lepidosiren presents very favourable opportunities. I have, however, 
made an exhaustive examination of the blood corpuscles of all the early stages, so that 
my observations extend over the whole history of the blood, from the time the first 
corpuscles appear in the heart onwards. I have necessarily studied the histogenesis 
of the spleen, and the development of the lymphoid tissue, so called, in the kidney, 
and have made incidental observations on the thymus gland. On this last head I shall 
have little to say, as [ hope soon to study the development of the gland in detail. 
For the purpose of the research, I have had the opportunity, through the kindness 
of my friend Professor GRAHAM Kerr, of going through the whole of the larval stages. 
This has involved the exhaustive examination of more than twenty series—up to stage 
No. 38 of the sequence, when the larva is already practically a small adult Lepidosvren. 
I have also examined sections of the modified filamentous hind limb of the male during 
the degeneration which ensues after the breeding season, when the tissues are crowded 
with leucocytes. 
As the result of these more extensive observations, I have not much to add in regard 
to the structure of the fully evolved elements. 
The erythrocytes in the adult and later larval stages have almost invariably a 
vesicular nucleus, and the few corpuscles that have a nucleus with the coarse reticulum 
of the earlier phases are to be regarded as young erythrocytes. ‘The equatorial band 
is less distinct in the adult corpuscles, and the reticular structure of the disc is more 
doubtful. The adult material is unfortunately not sufficiently well fixed to enable me 
to determine whether the reticular appearance of the adult corpuscle is wholly an artifact 
or not; but as the granular, irreeularly reticular appearance of the disc closely resembles 
that of the reticulum of the early corpuscles in a badly fixed condition, I think it 
probable that the larval and adult elements resemble one another in this respect also. 
I make, however, the same reservations in regard to this structural feature as I did in 
my previous communication. | find that the leucocytes of the adult and late larval 
Stages present no essential differences from those of the earlier stages described in 
Part I. I must add to that account, however, that I find forms with basophile granules. 
The cells containing these do not differ in general character from those with eosinophile 
granules, and, as in them, the granulation is either fine or coarse. I shall reserve what 
I have to say on the general morphology of the leucocytes until I have described their 
development. 
Before proceeding to the record of my observations, I must refer to certain general 
points. 
_* Complete historical accounts are given by CHoronscuHiTzky, Anat. Hefte, Bd. 13, 1900; and Piper, Diss. Med., 
Freiburg, 1902. See also specially Konumann, Archiv f. Anat., 1900. 
