CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
617 
observations suggest the inference, that the blood-making process in the examples of 
these Echinoderms is to some extent independent of floating cell-agency. The 
absence of proper-cells from vital fluids, attest to the physiologist a near approach, 
as respects the composition of such fluids, to the standard of an inorganic body. And 
the novel truth will flow from these researches, that, in structure and mechanism of 
nutrition, the living solids of the organism descend from the complex to the simple 
in the same degree as that in which the fluids may have fallen in the scale of vitality. 
During the examination of the fluids of other classes, the singular fact will be 
established that the chylaqueous fluid of the young of the Annelid, and of the larvae of 
some Insects, is scarcely, if at all, corpuscidated ; that the fluids become more and more 
charged with floating-cells the older the animal becomes, and that these cells actually 
change their structural characters as the growth of the animal advances. What is 
transitory in the Annelid and the Insect, may be the permanent condition in the 
Echinoderms. Then, the paramount question arises, in the absence of floating-cells 
from the fluids of the Echinoderms, in what manner are those fluids vitalized, raised 
from the inorganic to the organic condition ? It is probable that as all the fluid which 
reaches the visceral cavity passes through the digestive organs, and transudes the solid 
parietes of the latter, by which it receives the impress of the vital force from the 
living solids, its organic matter assumes the form of albumen and fibrine, which, 
incorporating with salt-water, becomes a vital fluid. 
The anatomy of the Holothuriadse and Sipunculidc3e places beyond controversy the 
correctness of the conclusions presented in the preceding pages, in relation to the 
real physiological meaning of the chylaqueous fluid in the inferior Echinoderms. 
In these orders the integumentary hollow membranous process more or less com- 
pletely disappears, and is replaced by the peculiarly fenestrated structure of the 
integuments formerly described in the Sipunculidae, to which is superadded a system 
of plumose tentacula or ramose cirrhi, which are confined to the cephalic extremity 
of the body. The real structure of these beautiful appendages has never yet been 
demonstrated. All naturalists have guessed that they fulfil a respiratory office. No 
observer has attempted to unravel the mechanism by which this office is accom- 
plished*. 
In different genera of these two orders, these appendages vary inimitably in num- 
ber and size and figure. Such external diversities are however accompanied by no 
structural and essential differences. In all species they constitute merely hollow 
* For confirmation of this statement I refer to all the recent works of French and English Comparative 
Anatomists, especially to Crochard’s edition of the ‘ Regne Animal.’ It is impossible that the true structure of 
the cephalic appendages of the Sipunculidm and Holothuriadse could have been determined without a previous 
knowledge of the real physiological signification of the chylaqueous fluid in the animal series. The organs 
destined to receive this fluid are strikingly different in structure from those designed to circulate true-blood. 
The cephalic appendages of these Verraigrade Echinoderms are not comparable in the remotest degree to the 
gills of fishes. Between them and the respiratory organs of some species of Annelida there is, however, a 
very intimate analogy. 
