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.^ 



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||, andholothuriae,^ 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. 



X In which the organs of motion are disposed as radii round a centre. 



§ Sea-blubber. 



|| Prickly-skinned zoophytes ; from 1%!**, a hedgehog, and St^«, the skin. 



% The Portuguese man of war. 



