TEREDO. 221 
appendages with them, whatever their nature may be. We 
will now consider the structure of the branchiz, and the 
surmises on the nature of the four brown cords that accom- 
pany them. 
The branchial apparatus is composed of only two narrow 
laminze 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 ani- 
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 m a nine-inch animal is from 4 to 44 
inches. The branchie im the livmg 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 branchiz 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 mvigorate the branchiz 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 branchiz ; but after 
all is said, their true functions are doubtful. 
With respect to the secretions, all that I know of them 
