170 SYSTEM OF AQUEDUCTS. 



sion of tlie parts forces the water again from the body by 

 the same channels. 



The discovery of this remarkable system of aqueducts 

 was made by the Neapolitan naturalist, S. Delle Chiaie, 

 not more than thirty years ago.* He detected it in many 

 testaceous and naked Gasteropods ; and ascertained that 

 there were no traces of it in some freshwater genera, as in 

 Limnaeus and Planorbis, — a singular exception, for which 

 probably you may find a reason in the comparative lightness 

 of their shells, requiring for their support no mechanical 

 additions to their inherent muscular powers. Delle Chiaie 

 found similar aqueducts in the arms of various Cephaloj)ods, 

 in whom they serve to elongate their motive organs, and to 

 distend their acetabula previous to their being fixed upon a 

 surface ; and the muscular fins of the Pteropods are perme- 

 ated by analogous canals. The discovery has been since 

 confirmed ; and the same apparatus has been shown to exist 

 in the Bivalves by Professor Baer, of Konigsberg ;-f- in many 

 Ascidians by Delle Chiaie ; ;|; and perhaps also in the pul- 

 monated terrestrious Gasteropods by M. Kleaberg, for this 

 seems to be the function of what he calls their "mucous 

 ducts." § It may, indeed, appear absurd to ascribe the office 



* Anim. s. Vert. Nap. ii. 259, &c. 



f The foot of Lucina " is frequently twice as long as the diameter of the 

 animal. When not contracted, it is much longer. It is remarkable that it 

 is hollow throughout its entire length, and that this tube opens directly and 

 widely into the spaces of the visceral cavity." — Forbes and Hanley's Brit. 

 Moll. ii. 42. 



X The curiously ciliated arms of the Brachiopoda arc extended by the 

 same means. When treating of Tcrebratula psittacea. Professor Owen says : 

 " The mechanism by which the arms are extended, is simple and beautiful. 

 The stems are hollow from one end to the other, and are filled with fluid, 

 which, being acted upon by the spirally disposed muscles composing the 

 parietes of the canal, is forcibly injected towards tlie extremity of the arm, 

 which is thus unfolded and protruded outwards." — Trans. Zool. Soc. i. 150. 

 See also, p. 155, where the Professor states that in Orbicula these canals 

 have no connection with the vascular system, 



§ "In the gasteropodous mollusca of the genera Limax, Arion, Helix, 

 and Bulimus, we find under the mouth, between the two inferior lips, and 

 the protuberance of the disk of the foot, the orifice of a canal, hitherto un- 

 observed, which runs along the whole of the foot. This anatomical arrange- 

 ment is not very distinct in the genus Succinea, which approaches nearer to 

 the Lymnsese in internal structure. In the Arion empiricorum, which is en- 

 tirely black, we perceive a trace of this canal, which appears in the form of a 

 whitish band. The canal is not simple ; it receives many little ducts, which 

 come from the muscular sac in which the viscera are contained. In the 

 Bulimus ovatus, Brug., a little gland, which has not been described, opens into 

 this canal ; it is of the size of a bean, trilobate, granulated, and situated under 

 the oesophagus and the inferior ganglion of the cerebral ring, so that it is sur- 

 rounded by nervous filaments passing from this ganglion. The distribution 



