TEREDO. 221 



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 accom- 

 pany them. 



The branchial apparatus is composed of only two narrow 

 laminae running horizontally from their origin, where they are 

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

 tapering gradually to the siphons ; but before they approach 

 them, for an inch or two, they become more fleshy and linear, 

 and are what Sir Everard Home terms " the strong substance 

 for the support of the weakest part of the body of the amv 

 mal " they do not enter the siphon, as in Pholas, being cut 

 off" therefrom by the posterior sphincter ; their colour is red- 

 dish-brown, and the blood, as seen by the microscope, very 

 pale pink ; their length in a nine-inch animal is from 4 to 4 

 inches. The branchiae in the living animal are doubled 

 together and hang on each other, but without the inter- 

 vention of any substance between them, and in this respect 

 are 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 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 

 will 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 excavation: 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 



