186 HUGH WATSON. 



same way as it does in Apera. In Euglandina we 

 have an intermediate arrangement, as will be seen from 

 Strebel's figures ^ ; for the structure that he described and 

 figured as a median odontophoral nerve from the ventral 

 group of ganglia, is, in reality, the buccal artery, as I have 

 found from an examination of E. venezuelensis {Preston). 



The pedal artery runs backwards above the pedal gland, to 

 which it gives off branches on each side. In Apera gib- 

 bonsi, A. dimidia, and A. sexangula, I have found a very 

 slender vessel uniting the anterior aorta with the pedal artery 

 about half way along the pedal gland (PI. XIII, figs. 52, 54, 

 and 57). After uniting w4th the terminal vesicle of the pedal 

 gland, the pedal artery continues backwards and downwards, 

 and becomes more or less embedded in the muscular con- 

 nective tissue of the foot. 



The venous system is largely lacunar, apart from the 

 pulmonary veins already described. Indeed, the only well- 

 defined vessel containing venous blood is the body-cavity itself. 

 I have already dealt with the dermal veins and their curious 

 sphincters, when treating of the structure of the skin." 



THE EXCRETORY SYSTEM. 

 The pericardium communicates with the mantle-cavity by 

 means of a single renal coelomoduct, divided into an ascend- 

 ing glandular portion, which forms the kidney, and a 

 descending non-glandular portion, which forms the ureter. 

 It will be seen from PI. IX, figs. 27-31, PI. XI, figs. 34, 35, and 

 PI. XII, fig. 36, that the kidney is applied to the left side of 

 the pericardium, and also extends over its posterior part 

 towards the right side, thus broadly connecting the peri- 

 cardium with the Avail of the mantle-cavity, with which the 

 kidney fuses a little further back. Ventrally the kidney is 

 prolonged backwards in the floor of the mantle-cavity on 



' 'Beitrag z. Kenntn. d. Fauna Mexikan. L.- u. Siisswasser-Conchylien,' 

 1878, vol. iii. pi. xvi, fig. 5, pi. xviii, figs. 1, 6. 10; pi. xix, fig. 1, pi. xx, 

 fig.l. 



* See pp. 126. 127. 



