Chylo-aqueous Fluid of Invertebrate Animals. 343 



those classes, as in the Echinodermata, Entozoa, and Annelida, in 

 which, in the adult animal, these two orders of fluids coexist, though 

 distinct, in the same individual, there prevails between them, as re- 

 spects their magnitude or development, an inverse proportion : that 

 while, as instanced in the Echinoderms, the chylo-aqueous fluid filling 

 the ciliated space between the stomach and integument is consider- 

 able in volume, the blood-proper and its system are little evolved ; 

 that while, as in the Entozoa, the chylo-aqueous fluid is still the 

 most important fluid element in the organism, the blood system is 

 proportionally rudimentary ; that in the Annelida, especially the 

 higher species of that class, the chylo-aqueous fluid almost disap- 

 pears, while the system of the true blood acquires, illustrating the 

 law of inverse proportion, a correspondingly augmented development. 

 The author then states, that the system of the chylo-aqueous fluid 

 does not exist in the adult, but only in the larva state of the higher 

 members of the articulated series, such as the Myriapoda, Insecta, 

 and Crustacea. 



In myriapods and insects, he has observed that the peritoneal 

 space is occupied by a fluid which does not communicate with, and 

 is distinct in composition from, the contents of the true bloodvessels. 



This peritoneal fluid, however, in these classes, disappears at a 

 subsequent stage of growth. Thus the author thinks, that a con- 

 tinuous chain through the medium of the fluids, is established be- 

 tween the Echinoderms at one extreme, and the Crustacea at the 

 other. These classes he proposes to connect together under the de- 

 signation of the double fluid series, corresponding to the radiate and 

 articulate series of systematic zoologists. 



Returning to the standard of the Echinoderms, where the system 

 of the blood-proper first' appears in the zoological scale, he shews 

 that at this point the Molluscan chain diverges from the radiate and 

 articulate chain, and may be indicated in contradistinction from the 

 latter, as the single-fluid series. The author's observations lead him 

 to believe, with Professor Milne-Edwards, that in all Molluscs, from 

 the Tunicata to the Cephalopods, the chamber of the peritoneal is 

 continuous with the channels of the circulation, and that consequently 

 the fluids observed in these parts, are one and the same fluid, esta- 

 blishing the singleness of the fluid system of the body ; and this con- 

 clusion is corroborated by additional evidence drawn from micro- 

 scopic examinations. 



He then recapitulates the results of his researches, and maintains 

 that the base of the invertebrated kingdom of animals is formed of 

 all those inferior series which rank below the Echinoderms ; and that 

 this series is distinguished from the Molluscan, in which also the 

 fluid system is single, by the important circumstance that in the 

 former, unlike the Mollusca, the digestive and circulatory systems are 

 identified, or confounded into a single system ; that at the Echino- 

 derms, the series divaricates into the double-fluid series and single- 



