RAMANAN : ON THE HABITS OP AMPULLARIA. 109 



contrary, the chief feature in the breathing process of our species lies in the 

 fact that the siphonal tube, after it has reached the top, increases enor- 

 mously in calibre at the expense of length. The orifice maintains this 

 diameter, as a rule, till the completion of the aerial respiration, and slowly 

 contracts afterwards till the lumen comes to be only 5 millim. in diameter. 

 Bouvier and Fischer make out that A. insulorum, d'Orb, the same species 

 with which Semper experimented, produces in the pulmonary sac move- 

 ments of ex- and inspiration, by alternately raising and depressing its head 

 inmuchthesamemanner as the Cetacea. But this does not occur in the 

 Madras species. The breathing-in is a process of complete suction, induced 

 or occasioned by the dilatation of the pallia! cavity, which, in the absence 

 of aerial respiration, is completely shrivelled up. So far from ever moving 

 its head at all, it hes perfectly c[uiet, keeping its tentacles loose and motion- 

 less, curled either round the margin of the foot or within the constriction 

 between the podial region and the shell.. The siphon meanwhile regains 

 its original length, the animal closes the aperture in the oblique septum 

 between the pulmonary sac and the branchial cavity, lowers the siphon 

 and admits water into it for aquatic breathing. Professor Semper, 

 in respect to the aquatic respiration immediately following the aerial one, 

 at the surface of the water, says that the A. insulonim, d'Orb., " reverses 

 the margin of the mantle, opening the tube into which the water streams." 

 So far as I have been able to make out, there is no reversion of 

 the rim of the pallial lobes at all in A. globosa. Swains. What takes place 

 is briefly this. The extremely broad orifice through which air enters, be- 

 comes somewhat contracted, the siphon regains its length by the infolding 

 of the nuchal lobe, and is lowered bodily under the water, and aquatic res- 

 piration begins. Another change is restricted to the circular aperture 

 in the roof of the mantle-cavity, communicating with the pulmonary 

 chamber above. It closes when the aerial respiration is over and the 

 animal lets down the siphon. To sec this aperture in the living state, 

 one has to suddenly seize an animal crawling on land, and before it has had 

 time to close its operculum, to force the latter the other way, when a 

 circular opening in the septum (lower wall of the pulmonary sac) can be 

 seen, contracting and expanding. As a rule, the animal does not abso- 

 lutely close the siphonal orifice when lowering it under water, only the 

 diameter of the orifice is lessened. But it closes it at once, if, on account 

 of some external disturbance, it is obliged to suddenly sink to the 

 bottom. The explanation of this is simple : it wants to avoid the ingress of 

 water, through the unclosed aperture in the septum, into the pulmonary 

 cavity, and therefore completely shuts the siphon. There is no doubt that 

 this contraction and expansion of the aperture which takes place when the 

 animal is on land, or when it is in water respiring air, has a respiratory 

 significance. And when the siphonal orifice is diminished in size, and 

 then lowered into the water, it is probably to suit the exigencies of aquatic 

 breathing. After a time, the animal again extends its siphon above the 



