CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
599 
circulation. Mr. Hancock and Dr. Embleton have shown that collateral segments 
of the circulation undergo a special elaboration for special or local purposes. They 
do not however demonstrate in any part of the blood’s circuit a peripheral capillary 
system. They only state that ‘‘ the existence of true capillaries in the liver-mass seems 
probable.” In further elucidation of the tendency to special development in parti- 
cular portions of the circulating system of mollusks, I have lately proved that the 
branchial capillaries in both the univalve and bivalve orders conform with singular 
constancy to one type of subdivision. The vessels are always parallel, never reticu- 
late. These observations support the proposition formerly stated, that in the Mol- 
lusca the circulating system is really a product of the fusion of the chylaqueous 
system into that of the blood, properly so called. In a letter addressed to M. Milne- 
Edwards, Mr. Huxley observes, after an examination of the circulation of the blood 
in the genera Firole and Atlante, “ J’ai obtenu ainsi une confirmation entiere de 
VOS vues relatives a la maniere dont cette fonction s’exerce chez les Mollusques. 
...II n’existe point de veines quelconques . . . Je suis porte a croire que I’absence 
plus ou moins complete de la portion veineuse du systeme vasculaire, loin d’etre un 
cas exceptionnel, est I’etat normal dans la plupart des classes de la grande division 
des animaux sans vert^bres*.” It is however to the ‘ Mernoire’ of M. Quatrefages, 
“ ISur la cavite generale du corps des Invertebr^s,” Annul, des Sciences Nat. 1850, 
that, in this historical summary, special attention is invited. In this excellent essay 
M. Quatrefages first describes “ la cavite generale du corps” as beginning with the 
Hydrse and Actiniae, and closes the survey with the Mammalia, the serous cavities of 
which he likens to the visceral cavity of the body as it is found to exist in the Inver- 
tebrata. In the mere description of ‘ the cavity’ there is no novelty. To all compa- 
rative anatomists for half a century the existence of the visceral cavity in the several 
classes of the Invertebrata has been familiar. To every observer it has long been 
well known that this cavity in all classes was occupied by a Jluid. On this ground 
therefore no modern anatomist is entitled to the credit of discovery. In the year 
1741, Trembley A’flie and accurately described the movement of a corpusculated fluid 
in the perigastric cavity and tentacles of the ‘ Polype ^ Panache.’ But in the memoir 
“Sur la cavite generale du corps des Invertebr4s,” M. Quatrefages has sagaciously 
projected certain generalized views with regard to the possible functions devolving 
upon the fluid contained in this cavity, which to a limited extent run parallel with 
the conclusions which in this paper I have endeavoured to establish. It will however 
be readily seen by any one who will peruse the two essays with a view to a com- 
parison, that they differ essentially in subject and object. M. Quatrefages’ chief 
aim is to define the visceral cavity; he adds only a few general observations with 
reference to the physiological relations and functions of the fluid contents. He has 
not attempted to resolve the problem of its histological characters. His conclusions 
* Observations sur la circulation du sang chez les Mollusques, des genres Firole et Atlante, Ann. des Sc. 
1850 . 
