212 



THE ACEPHALA. 



^195. 



§ 195. 



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

 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 ficts in its favor. 



^\hen 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 either 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 oP Soleyi,^^^ 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 ajjpear to be without walls, and have, in general, the aspect of 

 simple lacunae traversing the parenchyma of difi"erent 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- 



Janus, Isis, 1819 ; Treviranus, Beobacht. ic. p. 

 44. and the beautiful figures of Poli, loc. cit.* 



1 Baer was the first to call the attention to this 

 aquiferous system with the Naiades (Froriep's neue 

 Not. No. 265, 1826, p. 5) after an analogous one 

 had been pointed out with the Gasteropoda by 

 Delle Chiaje. Poli, it is true, had recognized it 

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

 cheae and partly for lymph oi blood-vessels. 



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

 went certainly too far when he affirmed that these 

 orifices are only accidental fissures. I have been 

 unable 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 tracheal 

 system. 



3 Orifices of this kind have been described and 

 figured by Delle Chiaje with Solen siliqua, as 

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

 1'). These pores communicate probably with an 

 aquiferous system which Treviranus has seen in 

 the foot of Solen ensis (Die Erschein, 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. 

 XX.X VII. fig. 1, S.) has figured as a Trachea. 



•'< 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, belong» 

 probably to the aquiferous system. The same in- 

 terpretation ought perhaps to be put upon a san- 

 guineous net-work which he has figured in the man- 

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

 oje (Uescriz. &c. III. Tav. LXXV. fig. 6, Tav. 

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



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

 ial vessels of Teredo, and beautifully illustrated, 

 see Deshai/es, loc. cit. p. 69, PI. VII. and (^uatre- 

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

 Williams, On the Structure of the Branchiae and 

 Mechanism of Breathing in the Pholadcs 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 bloixi of all lamellibranchiate mol- 

 lusca is richly corpusculatcd. 



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

 posed of straight parallel vessels returning upoa 

 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 linear se- 

 ries on either side of the branchial vessel, causing 

 currents, which set in the direction of the current 

 of the blood in the vessels." — Ed. 



