KESPIRATORY MECHAX'ISM OF THE AMPULLAEIID.E. 341 



17. Notes on the Respiratory Mechanism of the Anipullariida^. 

 By Guy V. IIobson, M.A., F.Z.S. 



(Offered tbv publication bj' pennissiou of the Trustees of the British Museiam.) 

 TReceived Tebrurtry 21, 1922 : Read February 21, 1922.] 



During- the latter pai't of tlie last centur}- a good deal of work 

 was done upon the respiiution of the amphihioiis gastropod 

 Ampullaria. The studies of Bavay, Sahatier, Bouvier and Fischer 

 together with the more recent work of Ramanan yielded a 

 satisfactory general account of the process. The method by 

 which the gill and lung are alternatively employed, the con- 

 ditions under which one or the other becomes functional and 

 the relation of the circulation to the I'espiratory orgaris are there- 

 fore fairly well known. There are, however, several details upon 

 which the older accounts are vague, and certain features seemed 

 so inexplicable that the donation by Colonel Knight and Colonel 

 Porteous of living examples of A. vermiforinis to the Society, 

 ■afforded a very welcome opportunity for fresh study. 



The general phenomena of pulmonary and bi^anchial respiration 

 recorded by Jourdain (6), Bouvier and Fischer (3), and Bavay (1) 

 for various Neotropical forms are found to take place in A. vermi- 

 formis. There is no need, therefore, to describe the details Avhich 

 may be found in the tuo latter papers. Bavay described three 

 types of respiration, and I propose to use the term ' siphonal ' for 

 the one in which air is drawn into the lung through the siphon 

 while the animal is still under water. It is to be distinguished 

 from ordinary branchial respiration on the one hand and from 

 direct pulmonary respiration on the other. 



A. The first point upon which fresh evidence may be offered 

 is the function of the longitudinal ridge ( ' repli palleal' ) Avhich 

 sub-divides the pallial cavity. Jourdain, Bavay and others speak 

 •as though the pallial cavity were divided into two separate parts 

 by the ridge in question which runs up the floor of the cavity 

 parallel to and on the left-hand side of the gill and rectum. The 

 precise role of such a division is not specified by previous workers ; 

 but one is left with the distinct impression that this apparent 

 division of the mantle-cavity into right (branchial) and left 

 (pulmonary) areas is of impovtaiice in respiration. The available 

 facts, however, appear to indicate that this is not the case. To 

 seal effectually the 'pulmonary' pallial chamber from water or the 

 branchial chamber from air, the separation of the two chambers 

 should be complete. But in over twent}^ examples of various 

 species and genera I have never found the ridge nearly high 

 enough along its entii'e length to touch the pallial roof. Bavay, 



