200 THE ACEPHALA. § 185. 



With both the simple and the compound Ascidiao, there are, atthebaseof 

 the oral tube and at the entrance of" the re»|)irator3- cavity, numerous fili- 

 form and sometimes fringed tentacles inserted upon a kind of ring.*" 

 With the Lamellibranchia, there arc often conical tentacles around the 

 respiratory and anal o}ienings of the mantle,'-' and the orifice of the 

 siphon.' ' Among those w liicii have an 02)en 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 brisfles 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 

 Mannnalia. 



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. ''^' 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 See the figures in Savigny, M^m. &c. loc. cit. Pr.ctnnciilus, Mactra, Anodonta, Aspergillum, 



2 Cardium, Chama^ Tridacna, and Isor.ardia. &c. But Spondylus and Pecten form, in this re- 



3 Solen, Pliolax, Aspergillum, Mactra, Venus, spect, an exception. Here, the lobes upon each side, 

 Oonax, kc. With Donax trunculiis, the res\m-- instead of being continuous, are separated by nu- 

 ;itory tulje is remav,v,tlp|: fur its raniiiied teutaclL'S ; inerons curioujly-brai f'sd tentacles which sur- 

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



* Unio, Anodonta. surrounding the mouth of certain Ilolothurioidae 



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



of tentacles is .'single ; but it is multiple with Atic- 8, 13, \i, XXVII. fig. 6, 10. 



ula, Anoinia, Ostrea, Pecten, Spondylus, ixad 9 The branchial lamellae of the Lamellibi'anchia 



Liimn. have these furrows upon all their siu"faces, and 



C So'e Oicen, and Vofct, loc. cit. in their outward aspect closely resem!)li; tli.'se lac- 



7 As to the oblong organ which, with A'a//)rt cordi- tile lobes. It is therefore probable that, like the 

 formix. projects into the cavity of tlie body as oral tentacles of the Polyps and II olothurians, they 



two parallel cutaneous folds between the anterior have a varied function. Thus, tlnj' could str\'e not 



respiratory opening and the central mass of the only as gustatory organs for the food ent-ring the 



nervous system, I am yet undetermined whether or mouth, but also as those of ingestion, ))esidc talciiis; 



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



libranchia. It appears smooth upon its free 10 The rese;\rches of Cuvier, Owen, and f'ogt 



border, 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 jirescrved in alcohol. 



Salpa zonaria, a similar organ lies directly in The relations, therefore, of these organs ami 



front of the central nervous mass ; &ee Eschric/it, their fringes during life are not known. Miiller 



Over Salperne, loc. cit. p. 14, fig. 8, 10, 22, t. AVith also (Zool. Panica,!. j). 4), and Puli (loc. cit. II. p. 



Salpa mucronata, this singular organ is situated 190, Tal). XXX. fii 22, 2o), say nothing upon the 



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



by JWe^en for a male genital organ ; see Ueber die tula. If they are really contractile and ciliated, 



Salpeu, &c., p. 307, Tab. XXVlIi. fig. 5-10. the whole apparatus is quit* analogous to that d 



8 Avicularia, Isocardia, Pinna, Cardium, the Alcyonellac. 



