ON THE CIRCULATION IN THE INVERTEBRATA. 
By Langston Parker. 
All animals possess a series of organs by which the fluids which are the 
product of digestion are distributed to the various parts of the body, to serve the 
purposes of nutrition and support. The sum of the actions of these organs is 
termed circulation ; and the aggregate of parts by which it is performed, the vas¬ 
cular system. In the whole animal series the organs of circulation are infinitely 
varied, bearing a strict relation to the degree the animal holds in the scale of 
being, to its mode of life, and the number of internal organs it possesses. In the 
lower animals, we find their bodies everywhere impregnated with fluids which are 
not contained in distinct canals, but pervade every part. In a higher grade, the 
fluids are contained in distinct canals; in the course of these canals are situated, 
in certain classes, organs which receive and propel the circulating fluids, for the 
purpose of giving them an activity and force of movement not impressed upon 
them by their mere containing vessels. In vertebrate animals, these organs are 
termed hearts, and are variable in the four orders of vertebrate animals in their 
number, their situation, and mode of action. In this paper I shall notice the dis¬ 
position of the vascular system, and the peculiarities of the circulation in the inver¬ 
tebrate classes of animals ; tracing them from the simple Zoophyte through the 
numerous families of molluscous and articulated animals, which are comprehend¬ 
ed in the system of Linneus, in the two grand classes of insects and worms, and 
by Cuvier in the three classes of articulata,* * * § mollusca,f and radiata.J: 
In the zoophytes there is no true circulating system. In the infusoria, polypes, 
and the inhabitants of corals and sponges, the uniform gelatinous granular mass of 
which the body is composed, is universally impregnated with fluids, and the func¬ 
tions of composition and decomposition, in the opinion of Carus, are performed by 
mere elective attraction and repulsion dependant on organic laws. In the medusae,§ 
echinodermata||, and holothuriae,<f[ a rudimentary class of vessels has been described 
by Cuvier, which opening from the intestines, pass either towards the organs of 
respiration, or towards the surface of the body, which in these instances is probably 
a respiratory organ as the skin is, in some degree, in certain reptiles. 
* Animals in which the general envelope of the body is divided, by transverse folds, into 
a certain number of rings. 
*f* Animals with a soft contractile skin, destitute, as the articulata, of a skeleton. 
$ In which the organs of motion are disposed as radii round a centre. 
§ Sea-blubber. 
|| Prickly-skinned zoophytes; from &x‘ vo h a hedgehog, and the skin. 
if The Portuguese man of war. 
