Royal Societij. 149 



ment. 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 blood -vessels. 



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 exti'eme and the Crustacea at the 

 other. These classes he proposes to connect together under the 

 designation 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 shows 

 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 perito- 

 neal is continuous with the channels of the circulation, and that 

 consequently the fluids observed in these parts are one and the same 

 fluid, establishing the singleness of the fluid system of the body ; and 

 this conclusion is corroborated by additional evidence drawn from 

 microscopic 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 system 

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

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

 fluid series, the former coinciding with the radiate and articulate 

 class, and joining the Vertebrata through the Crustacea; the latter 

 running parallel with the Molluscan order, and connecting itself to 

 the Vertebrata through the Cephalopods. 



The fluids of tlie zoophytic series are invariably corpusculated, 

 but the corpuscles cannot yet be reduced to any definite type of 

 conformation. In the Medusan series these bodies become more 

 definitively organized. The author then demonstrates, that through- 

 out the whole radiate and articulate classes, wherever it is found, 

 the chjlo-aqueous fluid is richly corpusculated, or in other words, 

 charged with floating morjjhotic elements, which, from the constancy 

 of their cliaractcra in different species, become grounds for specific 

 distinctions. It is stated, that, throughout the Echinoderms, En- 

 tozoa and Annelida, in which, even in the adult animal, the blood- 

 proper and the chylo-aqueous fluid, though separate, coexist, the 

 latter fluid only 13 corpusculated, the true blood being invariably 



