334 Mr. W . Clark on the Pholadidse. 



terminate with the larger ones at the siphons ; the addition of 

 the two shorter and smaller cords springing from the larger at 

 the point where the branchiae begin, appears to show a connection 

 of these appendages with them, whatever their nature may be. 

 We will now consider the structure of the branchiae, and the 

 surmises on the nature of the four brown cords that accompany 

 them. 



The branchial apparatus is composed of only two narrow la- 

 minse running horizontally from their origin, where they are the 

 broadest, attached to the dorsal region of the mantle and taper- 

 ing gradually to the siphons ; but before they approach them, for 

 an inch or two, they become more fleshy and linear, and are what 

 Sir Evcrard Home terms " the strong substance for the support 

 of the weakest part of the body of the animal ;" they do not enter 

 the siphon, as in Pholas, being cut off therefrom by the posterior 

 sphincter ; their colour is reddish brown, and the blood, as seen 

 by the microscope, very pale pink ; their length in a nine-inch 

 animal is from 4 to 4i inches. The branchiae, when not in natural 

 situ and opened for dissection, appear as a plane, but in the living 

 animal are doubled together and hang on each other, but without 

 the intervention of any substance between them, and in this re- 

 spect similar to the branchiae of the Pholades when they have 

 cleared the body and become linear ; but in Teredo they are 

 altogether posterior to the body ; the branchial artery of each 

 lamina runs as is usual parallel, and just under their junction 

 with the body, in the closest connection with the granular cords 

 in question ; but each branchial vein runs parallel and decidedly 

 within the granular cords, and shows no connection with them 

 like the arteries. What then is the nature of these appendages, 

 particularly of the longer ones ? I am inclined to consider them 

 glandular bodies, which perhaps serve either as emunctories, to 

 carry off injurious matters from the blood, or as absorbents of 

 what is beneficial : I am quite at a loss to say which of these very 

 opposite views is most probable. I state another surmise : they 

 may be an aid to extract additional quantities of air to invigorate 

 the branchiae in the production of the utmost vitality for the 

 blood, to support the animal in the arduous labours of exca- 

 vation : in this view they may be considered as rudimentary 

 branchiae ; but after all is said, their true functions are doubtful. 



With respect to the secretions, all that I know of them has 

 been mentioned under the heads of the organs I have described, 

 except those of the ovary, which will be noticed in the next sec- 

 tion. These animals, like all the bivalves, are sti'ict hermaphro- 

 dites. The ovarium is a white glandular body entwined with the 

 liver, but as it approaches the pericardium it becomes a distinct 

 mass ; and what is unusual at this time of the year,^ 20th January, 



