CHYLAQUEOUS FLUID OF IN VEHTEBRA'l E ANIMALS. 
609 
Extreme care and caution are required to observe separately the true-blood. It 
can only be found in the circular vessel, embracing the oesophagus, immediately under 
the lantern. The real vessel is quite distinct from the circular band of bright red 
pigment, which in this species acute observers have mistaken for a veritable blood- 
vessel. It is very difficult to detect the presence of vessels along the edges or in the 
parietal substance of the intestine in the Echinus. The bright red pigmented cellules 
distributed through the tissues, sometimes seen in lines and reticulations, have 
nothing to do witli the i/ooc?-system. The fluid contained in the circular vessel 
around the oesophagus is colourless. Its cell elements are precisely the same as 
those of the fluid of the general cavity. It is more opake than that of the visceral 
chamber, from the presence of a greater number of minute molecules*. 
In the Echinus it has proved to me impracticable to isolate the vessel so accurately 
from surrounding structures as to be enabled to detect the presence of cilia on the 
internal lining membrane. The whole structural character of the vessel however 
leads me to this inference. Its parietes are not definitively organized like those of 
every other true vascular channel ; cell and areolar fibres constitute the elements of 
its parietal structure. The preceding considerations have brought me to the belief, 
that in the Echinidae, as in the Asteriadse, the blood-proper has acquired scarcely any 
distinctive and independent characters; that the system of conduits in which it moves 
is so rudimentarily organized as to receive its contents, in some manner yet undeter- 
mined, directly (not by an act of elective, secretive absorption, as in the Annelida) 
from the fluid occupying the visceral cavity; that the blood-vascular apparatus, 
developed only in its central segments, is designed only to concentrate the nutritive 
force of the chylaqueous fluid upon certain of the more important viscera ; and that the 
nutrition of the peripheral structures of the organism, such as the muscular, calca- 
reous and integumentary, is sustained under the agency, exclusively, of the chyl- 
aqueous fluid. 
In the Sipunculidan genera the blood-system is more conspicuous anatomically, 
although little more advanced physiologically, than that of the former families. 
nennt, von welchem zur Tentakelrinne ein Ast abgeht. Dicht darunter soli sich das ringformige Blutgefiiss 
befinden, welches jedenfalls leicht aufzufinden, zu injiciren oder aufzublasen ist.” It is no severity of criticism 
to lament that this description by the great modern anatomist is little in advance of the original statements cf 
Tiedemann. — Op. cit. Muller, Archiv, 1850. 
* “ Die Blutgefasse (der Echiniden) verhalten sich so wie es Tiedemann beschrieben. Um den Mastdarm 
her liegt der bekannte circulus analis dicht auf dem Skelet, auf dem er bei Echinus sinuose Eindriicke zuriick 
lasst, ohne Zusammenhang mit den Ambulacralcaniilen. Er hat sehr zarte Wande und das Ansehen eines 
venbsen Sinus. Er entspricht dem Gefasscirkel am Riicken der Asterien und steht in demselben Verhaltniss 
zum Herzen wie dort. Wo der Gefasscirkel an das Becken der Madreporenplatte anstosst, erhebt sich aus dem 
Gefasscirkel die Fortsetzung zum Herzen, welche sich vom Cirkelge/ciss aufblasen lasst. Um eine klare Vor- 
stellung vom Herzen zu bekommen, muss man es bei Cidaris untersuchen, es ist bei Cidaris ein welter, ganz 
gerader Canal mit dicken weichen Wanden. Nach oben setzt es sich in eine Arterie fort, welche in den arte- 
riosen Gefasskreiss des CEsophagus iibergeht.” — Anatomische Studien uber die Echinodermen, von J. Muller, 
Archiv, 1850. 
