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THE ACEPHALA. 



^195. 



§ 195. 



It now remains to speak of a particular system of canals traversing in 

 all directions the body of the Lamellibranchia, which as yet has been 

 called the aquiferous system, because it is supposed to serve for an internal 

 respiration like that of the tracheae of insects.'^' But, in the first place, 

 the existence itself of such a system has been denied, although there are 

 certain facts in its favor. 



When one of these animals is suddenly taken from the water, numerous 

 fine jets of water are seen to pass from these organs while the animal is 

 withdrawing its foot and the borders of the mantle within the shell. From 

 this fact it is evident that these orifices connect with aqueous reservoirs. 

 But these openings are very small and probably are closely contracted, for 

 they cannot be discovered cither before or after the jetting out of the wa- 

 ter.^-* Orifices of this kind have as yet been found in a few species only ; 

 such are those in the extremity of the foot of Solen,^^^ and that singular 

 tube found above the pedunculate anus of Pinna.^^^ 



The aquiferous canals themselves are not very apparent, being seen only 

 after injection. This last is easily performed by blowing through a small 

 tube inserted under the skin. There will then be seen a very beautiful net- 

 work of canals, which, nearly all of the same size, are spread out under 

 almost the whole skin and enter the interior of the body by larger canals. 

 These canals appear to be without walls, and have, in general, the aspect of 

 simple lacunae traversing the parenchyma of diiferent parts of the body. 



By some naturalists, this net-work of canals is regarded as a system of 

 lacunae circulating the blood ;'•''> but when they are inflated, another net- 



jfinus, Isis, 1819 ; Trevirnnn/s, Benhacht. &c. p. 

 44. and the beautiful ftyurts '.>r Pu/i, Idc. cit.* 



1 Baer was the first to call the attention to this 

 aquiferous system with the Nannies {Froriep''s neue 

 Not. No. 265, 1S26, p. 5) after an analogous one 

 had been pointed out with the Gasteropoda by 

 Delle Chinje. PoH, it is true, had recognized it 

 bolore this, but he had taken them partly for tra- 

 cheae and partly fur lymph oi blood-vessels. 



2 Meckel (Syst. d. vergleich. Auat. VI. p. 64) 

 went certainly too far when he affirmed that these 

 orifices are only accidental fissures. I have been 

 unal)le to find the orifices, which, according to Poli 

 (loc. cit. Introductio, p. 42, 52), are upon the summit 

 of the cirri of the mantle and lead into a traclieal 

 system. 



Ji Orifices of this kind have been described and 

 figured by Delle Chiaje with Solen si/iqua, as 

 Fori aquiferi (Descriz. &c. III. p. 60, Tav. XC. fig. 

 11). These pores communicate probably with an 

 aquiferous system which Treviramis has seen in 

 the fuot of Solen ensis (Die Krschein. u. Gesetze 



des organisch. Lebens. I. p. 276). The orifice 

 which Garner has figured upon the middle of the 

 foot of Psammobia and Cardium, and to which 

 he has given the name of Porus pedalis, belongs 

 undoubtedly to this system ; see Trans, of the Zool. 

 Soc. II. PI. XVIII. fig. 2, 13, f. 



4 I have easily inflated the reticulated aquiferous 

 canals of this animal by this tube, which, in Pinna 

 nobilis, sometimes protrudes far beyond the bor- 

 ders of the mantle, and which Poli (loc. cit. II. 

 p. 241, Tab. XXXVI. fig. 3, N. fig. 7, Z. and Tab. 

 XXXVII. fig. 1, S.) has figured as a Trachea. 



•5 See above § 192, note 11. The vascular net- 

 work which Poli (loc. cit. I. p. 8, Tab. IX.) has in- 

 jected with mercury in the mantle of a Unio, and 

 which he regarded as a lymphatic system, belongs 

 probably to the a<iuiferous system. The same in- 

 terpretation ought perhaps to be put upon a san- 

 guineous net-work which he has figure<l in the man- 

 tle of a Pinna (loc. cit. Tab. XXX VIII. ). Delle Chi- 

 aje (Descriz. &c. III. Tav. LXXV. fig. 6, Tav. 

 LXXVI. fig. 3, 6, and XC. fig. 1, 2, LXXXIX. H^^ 



* [ § 194, note 20.] For full details on the branch- 

 ial vessels of Teredo, and beautifully illustrated, 

 see Deshayes, loc. cit. p. 69, PI. VII. and Qtiatre- 

 fages, Memoire, loc. cit. p. 57, PI. II. See also 

 fFillianis, On the Structure of the Branchiae and 

 Mechanism of Breathing in the Pholades and other 

 Lamellibranchiate MoUusks, in the Report of the 

 Brit. Assoc, for the Advancem. of Sc. for 1851, p. 82, 

 His first four conclusions are : 



" 1. That the blood of all lamellibranchiate mol- 

 lusca is richly corpusculated. 



" 2. That the branchiae in all species are com- 

 jjosed of straight parallel vessels returning upon 

 themselves. 



" 3. That the heart is systemic and not branchial. 



" 4. That the parallel vessels of the gills are 

 provided with vibratile cilia disposed in a Unear se- 

 ries on either side of the branchial vessel, causing 

 currents, which set in the direction of the cuiTeut 

 of the blood iu the vessels." — Ed. 



