CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
643 
corpuscles of the Arachnid are capable only in a very slight degree of refracting 
light ; hence the peculiarly translucent and delicate character of these bodies. Jn a 
perfectly fresh state, and unmixed with any menstruum, they are readily defined. 
The cell-capsule is as undetectable as it is in the Crustacea. In Arachna grandis, and 
the common House Spider, illustrative examples may be easily obtained (Plate 
XXXIV. fig. 62 and 63). 
The conformity of the Arachnid blood-corpuscle to the normal articulate type is 
placed by these exan)ples beyond doubt. Thus is presented to the philosophic 
zoologist a new and unexpected order of affinities as valuable as those established 
through observed resemblances in the systems of the solid organs, and by which in 
future every scheme of classification must be either corrected or confirmed. The 
physiologist will now recognise in the mysterious unity of form and structure which 
pervades even a microscopic cell, floating detachedly in a fluid, an immutable law 
(jf organic continuity through which the thoughtful eye may trace relationships 
between animals far separated in the zoological series. 
Mollusca . — Cuvier, Owen, M.-Edwarus, and recently, and more minutely, Alder 
and Hancock, have, by their several researches, elucidated with great success the 
mechanism of the circulation in the Mollusca. To this department of the subject of 
this memoir, it is not in my power, at present, to make any considerable addition. 
It is remarkable, that, while studying the channels of t he fluids, the great observers 
named did not on any occasion digress to an examination of the fluids themselves*. 
In addition to the historical sketch formerly presented, it must here be stated that 
the most recent essay on the blood of Mollusks is that which has lately appeared from 
the pen of M. Moquin-Sandon'|'. This writer devotes some pages of his short paper 
to a discussion of the point whether the red viscid fluid which appears to escape fi orn 
the edges of the mantle of the Planorbidse when irritated, is blood or not blood. 
Having exhausted the controversy, he concludes that it is blood. “Examinee au mi- 
croscope,” he observes, “au moment oh elle sort de I’anirnal, on y remarque un 
certain nombre de corpuscles irregulierement arrondis, inegaux, tout ^ fait semblables 
aux globules sanguins des Gasteropodes. Leur diam^tre est de ^ et 3 ^ de 
millimetre.” It will be afterwards shown that the following propositions of Moquin- 
Sandon are contradicted by the best observed facts. “ 1 . Les Planorbes ont le sang 
rouge ou rougeatre ; 2 . Les tr^s petites esp^ces ont le sang rose on couleur de chair ; 
3. La liqueur repandue par ces Mollusques, quand on les irrite, n’est pas une humeur 
particuliere secrete par le collier, ni par tout autre organe, inais du sang mel 6 a la 
mucosite ; 4 . Le sang, epanche dans la grande cavit^ du corps des Planorbes, com me 
chez les autres Gasteropodes, se voit distinctement, pendant la vie, quand il est ties 
rouge, chez les esp^ces ^ coquille transparente ; 5. Le sang r4pandu par les Planorbes, 
quand I’animal se retire brusqiiement et profond^ment dans sa coquille, n’est pas 
* See ante. 
t Memoires de I’Acad^mie de Toulouse, 1849 ; and afterwards copied into the Ann. des Sc. Nat. 1851. 
-MDCCCLII. 4 O 
