608 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
No feat in anatomy is more practicable than in any species of Sipunculus, to 
bring under direct view in the field of the microscope, the blood-vessel which reposes 
on the oesophagus. Although more perfectly formed as a vessel, more defined in its 
parietes, than the circular vessel of the Asteriadse, it may be placed beyond doubt 
that its interior also is lined by vibratile epithelium ; that its contents are chemically 
and morphologically identical with those of the visceral cavity of the same animal. 
It maybe mentioned here as a remarkable fact, that in the Sipunculidse (at least 
such is the result of my examinations repeated with the utmost care upon many scores 
of living specimens) the vessel which rests upon one side of the oesophagus is not 
accompanied by a venous correlate on the opposite aspect of the cylinder, nor by 
one parallel to itself on the same side. It is a single channel, which cannot he traced 
to a distal system of capillaries. 
In the Sipunculidee there are no “ Polian vesicles” attached to or developed from 
this vessel. The appearance of “ vesicles” arises from the bulged knots into which 
the vessel irregularly contracts under the stimulus of the air at the moment of laying 
open the general cavity. To these facts, as illustrative of the singular conditions 
under which “the circulation of the blood” is first evolved in the ascensive progres- 
sion of animal structures, the highest physiological interest attaches. 
After this short historical inti oduction, the several characters of these three systems 
of fluids maybe more carefully examined. 
Blood-proper in the Echmoderms . — In the Asteriadee and Echinidae this fluid is 
colourless, and charged only with irregularly organized corpuscles ; when placed under 
the microscope, it is quite impossible to distinguish these latter from those found in 
the peritoneal fluid, or in the water-vascular system of the same individual. In Uraster 
papposa, as already stated, the circular vessel and the radial trunks are so large and 
accessible as to be readily injected. Two methods may be adopted to determine the 
presence of cilia on the internal lining membrane of these vessels. In a fresh speci- 
men a portion of the trunk may be cut out and laid under the microscope with a 
view to see through its parietes, a current of moving corpuscles driven along by 
vibratile cilia, or the vessel may be cut transversely into thin circular sections. These 
sections will exhibit cilia in active motion on both the outer and inner edges of the 
parietes of the vessel. In the Asteriadee the whole interior oi every organ (except the 
ovaries) in the body is coated with vibratile epithelium*. The blood of tlie Echinidae 
is also colourless. 
* In his recent essays, Muller gives no further account of the blood-vascular system in Asterias than that 
which occurs in the following scanty passage : — “ Das Wassergefasssystem zur Erection der Fiisschen und das 
Blutgefasssystem der Asterien sind vouTiedemann so vollstiindig und naturgetreu beschrieben, dass ich nichts 
dazu nachzutragen gefunden babe, als dass der unter der Haut des Mundes auf dem hiiutigen Discus liegende 
Blutgefassring, ausser den von Tiedemann angezeigten und abgebildeten Aesten auch zu jedem Strahl einen 
Zweig giebt, der wieder 2 kurze Seiteniiste abschickt, wie Tiedemann’s Nerven der Arme. Die Injection vom 
Blutgefassring gelang nur bis zum Anfang dieser Gefdsse.” In another passage he incidentally observes. 
“ Zunachst unter der Haut am Munddiscus liegt nach Tiedemann das, was er den orangefarbenen Gefiissring 
