200 THE ACEPHALA. $ 185. 
With both the simple and the compound Ascidiae, there are, at the base of 
the oral tube and at the entrance of the respiratory cavity, numerous fili- 
form and sometimes fringed tentacles inserted upon a kind of ring.® 
With the Lamellibranchia, there are often conical tentacles around the 
respiratory and anal openings of the mantle,” and the orifice of the 
siphon. Among those which have an open mantle, there are many the bor- 
ders of whose mantle, either wholly, or only posteriorly,” are provided with 
thickly-set conical tentacles. These receive all their nerves from those of 
the mantle. 
Instead of these retractile tentacles, the Brachiopoda have long radi- 
ating bristles upon the borders of their mantle. These project a consider- 
able way beyond the borders of the valves, and having perhaps sensitive 
nerves at their base, they are thus tactile organs like the vibrissae of some 
Mammalia. : 
The oral opening of all the Lamellibranchia is provided, moreover, with 
two pairs of contractile, foliated lobes, pointing backwards, which are per- 
haps oral tentacles.” Hach pair is composed of two lobules, an internal 
and an external, which are united at their base, and whose surfaces lie 
against each other. Behind, the border of these four lobes is somewhat 
thinned, while in front, the two on the same side usually pass into each 
other, the external being above, and the internal below, the oral opening.© 
The free surfaces of the lobules are smooth and covered with a very thin 
epithelium, while the other and opposite surfaces are furrowed transversely 
throughout, and the borders of these furrows are fringed with very large 
vibratile cilia. 
As tactile organs, may be mentioned the two remarkable arms which, 
with the Brachiopoda, are spirally rolled up near the oral opening. The 
jong, pectinate fringes upon their borders are united at their base by a soft, 
hollow membrane which is probably contractile, and is provided with vibra- 
tile cilia, 
1 See the figures in Savigny, Mém. &c. Joc. cit. 
2 Cardium, Chama, Tridacna, and Isocardia. 
8 Solen, Pholas, Aspergillum, Mactra, Venus, 
Donaz, &c. With Donax trunculus, the respir- 
atory tube is remarkable for its ramified tentacles ; 
see Polt, loc. cit. Tab. XIX. fig. 15-20. 
4 Unio, Anodonta. 
5 With Donax, Mactra, and Tellina, this row 
of tentacles is single ; but it is multiple with Avic- 
ula, Anomia, Ostrea, Pecten, Spondylus, and 
Lima. 
6 See Owen, and Vogt, loc. cit. 
7 Asto the oblong organ which, with Salpa cordi- 
Sormis, projects into the cavity of the body as 
two parallel cutaneous folds between the anterior 
respiratory opening and the central. mass of the 
nervous system, I am yet undetermined whether or 
not it corresponds to the tactile lobes of the Lamel- 
libranchia. It appears smooth upon its free 
border, and receives, at its transversely striated 
base, two nerves from the principal ganglia. With 
Salpa zonaria, a simiiar organ lies directly in 
front of the central nervous mass; see Eschricht, 
Over Saiperne, loc. cit. p. 14, fig. 8, 10, 22, t. With 
Salpa mucronata, this singular organ is situated 
dn front of the nervous centre, and has been taken 
by Meyen for a male genital organ; see Ueber die 
Salpen, &., p. 397, Tab. XXVIII. fig. 5-10. 
8 Avicularia, Isocardia, Pinna, Cardium, 
Pectunculus, Mactra, Anodonta, Aspergillum, 
&c. But Spondylus and Pecten form, in this re- 
spect, an exception. Here, the lobes upon each side, 
instead of being continuous, are separated by nu- 
merous curiously-branched tentacles which sur- 
round the oral orifice and strikingly resemble those 
surrounding the mouth of certain Holothurioidae 
when contracted; see Poli, loc. cit. Tab. XXIL fig. 
8, 13, 14, XXVIL fig. 6, 10. 
9 The branchial lamellae of the Lamellibranchia 
have these furrows upon all their surfaces, and 
in their outward aspect closely resemble these tac- 
tile lobes. It is therefore probable that, like the. 
oral tentacles of the Polyps and Holothurians, they 
have a varied function. Thus, they could serve not 
only as gustatory organs for the food entering the 
mouth, but also as those of ingestion, beside taking 
@ part also in the respiration. 
10 The researches of Cuvier, Owen, and Post 
(loc. cit.) upon the arms of the Brachiopoda, were 
made upon specimens preserved in alcohol. 
The relations, therefore, of these organs and 
their fringes during life are not known. Miuiller 
also (Zool. Danica,I. p. 4), and Podi (loc. cit. IL. p. 
190, Tab. XXX. fig. 22, 23), say nothing upon the 
motions of the fringes of Orbicula and Terebra- 
tula. If they are really contractile and ciliated, 
the whole apparatus is quite analogous to that of 
the Alcyonellae. 
