200 THE ACEPHALA. <$> 185. 



With both the simple and the compound Aseidiae, 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 oi"al tentacles.'"' Each 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 

 long, 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*^' 



1 See the figures in Savigny, Mim. &c. loc. cit. Pectunculus, Mactra, Anodonta, Aspergillum, 



2 Cardium., Chama, Tridacna^ and Isocardia. &c. But Spondylus and Pecten form, iu this re- 



3 Solen, P/io/as, Aspergillum, Mactra, Venus, spect, an exception. Here, thelobesupon each side, 

 Donax, &c. With Donax trunculus, the resiMr- mstead of being continuous, are separated by nu- 

 atory tube is remarkable for its ramified tentacles ; nierous curiously-branched tentacles which sur- 

 see Poll, loc. cit. Tab. XIX. fig. 15-20. round the oral orifice and strikingly resemble those 



i Unio, Anodonta. surrounding the mouth of certain llolothurioidae 



5 With Donax, Mactra, and Tellina, this row when contracted; see Poli, loc. cit. Tab. XXII. fig. 

 of tentacles is single ; but it is multiple with Avic- 8, 13, 14, XXVII. fig. 6, 10. 



via, Anomia, Ostrea, Pecten, Spondylus, and a The branchial lamellae of the Lamellibranchia 



Liima. have these furrows upon all their surfaces, and 



U See Owen, and Vogt, loc. cit. in their outward aspect closely resemble these tac- 



7 As to the oblong organ which, with Sa/pacordz- tile lobes. It is therefore probable that, like the 



formis, projects into the cavity of the body as oral tentacles of the Polyps and Holothurians, they 



two parallel cutaneous folds between the anterior liave a varied function. Thus, they could serve not 



res])iratory opening and the central mass of the only as gustatory organs for the food entering the 



nervous system, I am yet undetermined whether or mouth, but also as those of ingestion, beside taking 



not it corresponds to the tactile lobes of the Lamel- a part also in the respiration. 



.libranchia. It ajjpears smooth upon its free 10 The researches of Cuvier, Owen, and Vogt 



V>order, and receives, at its transversely striated (loc. cit.) upon the arms of the Brachiopoda, were 



base, two nerves from the principal ganglia. With made upon specimens preserved in alcohol. 



Salpa zonaria, a simiiar organ lies directly in The relations, therefore, of these organs and 



front of the central nervous mass ; see Eschricht, their fringes during life are not known. Müller 



Over Saiperne, loc. cit. p. 14, fig. 8, 10, 22, t. With also (Zool. Danica,!. p. 4), and Po/J (loc. cit. II. p. 



Salpa 7ni/.cronata, this singular organ is situated 190, Tab. XXX. fig. 22, 23), say nothing upon tho 



in front of the nervous centre, and has been taken motions of the fringes of Orbicula and Terebra- 



\>y Meyen for a male genital organ ; see Ueber die tula. If they are really contractile and ciliated, 



Salpen, &c., p. 397, Tab. XXVill. fig. 5-10. the whole a])paratus la quite analogous to tliat of 



6 Avicularia, Isocardia, Pinna, Cardium, the Alcyonellae. 



