1873.] 329 : [Morse. 
exist. ‘They do not open outwardly, at least, not so far as known at 
present. In the test of Lingula pyramidata, they are exceedingly 
minute, and closely crowded together. Dr. Gratiolet has also 
observed them in the test of L.hians. In Discina I have failed 
to find them. Dr. Carpenter,! who is one of the highest au- 
thorities on the subject, states that these tubules are intimately 
connected with the vascular layer, which sends cecal prolonga- 
tions into each one of them. Hancock questions this view, and 
states that from his observations, the cecal processes spring from 
the reticulated layer of the pallial membrane, though he admits the 
constant presence of corpuscles in the ceca, which strongly resemble 
the blood corpuscles. 
Hancock, in speaking of the tubules, says: ‘ The best mode of investigating 
these organs is to dissolve the shell, and then they are exposed in various stages 
of growth, adhering to the margins of the mantle. They are arranged in rows, 
and are cylindrical, with the distal extremity obtusely rounded, and are pedun- 
culated from the first; the peduncle is long and narrow; the cceca at the extreme 
edge are small, but rapidly increasing in size backward; the terminal, or en- 
larged portion, is almost constantly stuffed full with the so-called blood cor- 
puscles. When observed in this way, these organs have very much the charac- 
ter of secerning follicles, but what function they really subserve is difficult to 
determine; it may be that they have something to do with the growth and 
reparation of the shell, though it is not easy to understand how. They are 
probably, as suggested by Prof. Huxley, the homological representations of the 
vascular processes that penetrate the test of the Ascidian; and if so, it would 
seem likely that they have lost much of their functional importance; and, in 
fact, their entire absence in forms closely allied to those in which they are 
highly developed, augurs that they are not of high functional importance.” 
Albany Hancock, on the organization of the Brachiopoda. Trans. Phil. Soc., 
London, Vol. 148, p. 887. 
See also Prof. W. King, on the Histology of the test of class Palliobranchiata. 
Trans. Royal Irish Acad., Vol. xxiv, part x1, 1869. In some observations on 
the early stages of Terebratulina, I found the tubules in the very youngest 
stages of the shell.? 
Claparéde states that only worms with a thickened integument have 
those peculiar canals, and not even all these, and accordingly we 
find in Brachiopods, as worms with a thickened and indurated 
integument, that while many possess these canalicular tubes, in 
others they are quite absent. 
1Proc. Royal Soc. London, Vol. vil., p. 32. 
2 Memoirs, Boston Soc. Nat. Hist., Vol. 11. 
