394 Dr. T. Williams on the Mechanism of Aquatic 



is non-corpusculated. The converse is true of the chylaqueous 

 fluid. No instance is known in which it does not abound in 

 regularly and determinately organized floating cells. The phy- 

 siologist recognises in these facts the presence of experimental 

 conditions of the highest interest. When the branchial organs 

 carry blood, perfectly devoid of morphous elements of any 

 description whatever, yet fulfilling the purposes of breathing, the 

 floating cells of the fluids are shown to be 7iot necessarij to the 

 interchange of the gaseous elements concerned in this vital 

 process. On the basis of these unequivocal and visible facts, it 

 is not rash to erect the rule that the floating corpuscles of the 

 organic fluids enact no share whatever in the first stage of the 

 respiratory process, — that is, in that which comprehends the 

 mere ingress of oxygen and the egress of carbonic acid ; their 

 office, however it may be hereafter defined, has reference to the 

 subsequent assimilation of the oxygen with the proximate prin- 

 ciples of the blood. Through the instrumentality of the cor- 

 puscles tbis quickening element is probably coerced into chemical 

 union with the integral constituents of those principles from 

 which a new compound eventuates. 



No class of invertebrate animals unmasks so completely to 

 the eye of the scientific observer of nature the physical machineiy 

 through which the function of breathing is fulfilled as that of 

 the Annelida. Gifted with brightly coloured blood, every ra- 

 musculc of the blood system can be tracked to its finest extremes. 

 Nature is more comprehensible in her humblest efforts than in 

 her master-pieces. Her plans are susceptible of readier recog- 

 nition. The intentions of the faultless Artificer are less equivo- 

 cally apparent. Subtlety gives place to simplicity, obscurity to 

 light. 



The Annelids are emphatically inhabitants of the sea-shore. 

 They are seldom afloat. Always accessible in their littoral 

 haunts, they invite the zootomist to demonstrate in their orga- 

 nization those abstruse theorems of vital dynamics which in 

 other beings transcend the genius of science. 



The branchial appendages in the genus Serpula are grouped 

 in erectile tufts around the head. Projecting in a comb- like 

 form from the cephalic extremity, and tinted variously and 

 beautifully in di0"erent species, they are admirably adap d for 

 the exposure of the blood to the agency of the surrounding 

 water. Each process is supported by a camerated frame or basis, 

 large and distinct at the thick edge of the comb, from which, 

 on one side only, projects a double row of secondary processes. 

 This supporting framework is composed of an extremely flexible 

 and delicate cartilage, the chambers of which are filled wi h a 

 limpid fluid which is in communication with that of the peritoneal 



