40.4 Oti the Mechahism of Aquatic Respiration. 



EXPLANATION OF PLATE XIV. 



Fig. \. (A.) Cephalic end of the body of Terebella nehulosa, laid open to show 

 the afferent vessel {d) and efferent vessel (e) of the true-blood 

 branchia; («) ; e, denotes a corpuscle of the chylaqueous fluid 

 filling the peritoneal cavity of the body, and communicating di- 

 rectly v\ith the hollow axes of the tentacular filaments (6). 



Fig. 2. exhibits the extreme end of one of the tentacular filaments (6, A) 

 viewed by transmitted light ; /, vibratile cilia ; g, ditto, covering 

 the under surface ; i, a true-blood-vessel floating in the chyl- 

 aqueous fluid, of which the corpuscles are seen rolling out at (j). 



Fig. 3. Extreme division of one of the true-blood branchiae (a. A); i, afferent 

 vessel dividing dichotomously, returning upon itself at m, and 

 ending in the efferent vessel (k) ; a^ &,n, mark the thin, contractile 

 envelope by which the vessels are embraced. 



Fig. 4. Foot and branchial appendage of Eunice margaritacea : m, afferent 

 vessel entering the base (a) of the branchial process, of which 



b, c, d, e,f, are five vertical branches. Each branch as seen at fig. 5 

 consists of a single vessel (i) returning in a looped manner upou 

 itself {j} ; g, cirrus of superior foot ; h, inferior foot ; g, inferior 

 cirrus. 



Fig. 6. Foot of Syllis (Williams*) : e, cavity enclosed by the foot and 



filled with the chylaqueous fluid (fZ); e, vibratile cilia clothing the 

 exterior ; a, branchial process ; /, its lacunose tissue ; e, exterior 

 cilia. 



Fig. 7- (A.) Foot of Nepht/njs Hombergii : a, branchial process, depending 

 in form of cirrus from the base of the superior foot : (B.) an en- 

 larged view of the branchial process examined as a transparent 

 object. It consists of a lioUow process filled with the chylaqueous 

 fluid, in the midst of which is seen floating a long, undividing, 

 complexly coiled true-blood-vessel (c). The process is lined 

 externally by a ciliated epithelium. 



Fig. 8. Vertical view of the foot of Nerine vulgaris : k, cavity enclosed by 

 the base ; m, cor})uscles of the chylaqueous fluid by which it is 

 filled; h,f,g, channels penetrated by the chylaqueous fluid in the 

 fleshy lobules ; i, true-blood-vessel occupying the hollow of the 

 process ; c, d, flat cirri of the upper and lower feet ; o, cilia ; 

 a, b, integuments. 



Fig. 9. Clymene Ebiensis : a, mouth ; b, first row of hooked seta; ; 



c, branchiae jirojecting from the tail ; B, one frill of the branchial 

 process detached and viewed transparently ; e, f, corpuscles of 

 chylaqueous fluid by which the lobules are filled ; d, true-blood- 

 vessel floating in the fluid. 



Fig. 10. A part of the mid- body oi Nais filiformis viewed by transmitted 

 light — showing the same precise relation between the chylaqueous 

 fluid (e) and the true-blood-vessels (/,/) as exists in the branchiic 

 — proving that although the parts are internal, the conditions of 

 respiration are complete : a, intestine ; b, c, dorsal and ventral 

 primaiy vessels ; d, cavity of the body. 



This species will be described in a future number of the 'Annals. 



