100 E. RAY LANKESTER, ON THE 
gain a very definite view of the probable homologies of the 
two fluids in the earthworm, but it is not yet apparent which 
of the two should be called “ blood,” and recognised as the 
homologue of that fluid in the vertebrata—whether that which 
represents the sauguineous system of Insects, or the red fluid, 
homologous with the water-vascular system of Scolecida. 
The following view, which tends to explain the matter and 
place it in a clear light, is put forward by my friend Pro- 
fessor Busk. In vertebrata the blood can be separated into 
two parts—the red corpuscles and the clear white plasma with 
the white corpuscles. The function of the red corpuscles, it 
is generally admitted, is to carry oxygen—in fact, is respira- 
tory. The function of the plasma, on the other hand, with 
its white corpuscles, is simply nutrient. Assuming that this 
is a correct view of the case, since it is supported by many and 
conclusive facts, and, indeed, is very generally conceded, let 
us turn to the Annelida. We find a red fluid, undoubtedly 
devoted to respiratory purposes in many genera, and a colour- 
less plasma with white corpuscles, bathing all the organs of 
the body. ‘The conclusion is, obviously enough, that the red 
vascular fluid represents simply the corpuscles, whilst the 
colourless corpusculated fluid is homologous with the white 
plasma of vertebrate animals. It would be unsafe to draw 
any conclusions as to the respective functions of the fiuids 
from this comparison. The functions of the two fluids 
in the Annelida have yet to be much studied, all that zoolo- 
gists at present appear to be agreed upon being that the 
red vascular fiuid is the chief medium through which re- 
spiration is effected ; how far this function is shared by the 
corpusculated fluid, or how far nutrition is also a part function 
of the red fiuid, are questions to which no decisive reply has 
yet been offered, though the considerations above adduced 
would tend (perhaps erroneously) to the conclusion that re- 
spiration belongs to the one and nutrition to the other 
exclusively.* In speaking, then, of these two fluids, I prefer 
* M. Milne Edwards, in the remarkably exhaustive and valuable work, 
which he is now completing, commenced in 1857, and entitled ‘ Legons sur 
la Physiologie,’ adopts, to a great extent, the view advanced first by De 
Quatrefages, and used aftewards, more or less, by Dr. Williams, that in the 
Annelida, as a rule, the perivisceral fluid becomes oxygenated and transfers 
its oxygen to the vascular fluid, which, however, in other cases may become 
directly oxygenated by the direct contact of its containing vessels with ex- 
ternal fluids. He also considers the vascular fluid as having a nutrient 
function (vol. ii, p. 95; vol. iii, p. 239). 
Professor Huxley, on the other hand, is inclined to regard the system of 
vessels in which this usually red fluid is contained as an extreme modifica- 
tion of the water-vascular system of Trematoda and Cestoidea, which is by 
M. Milne Edwards considered as an excretory apparatus, by others as 
