182 HUGH WATSON. 



part of the body-cavity, as in Natalina, Rhytida, Pary- 

 phanta, Schizoglossa, Testacella, Streptaxis, 

 At op us, and a few other carnivorous genera, and is only 

 held in position by the pedal artery which supplies it with 

 blood. This artery confines the gland to the anterior part of 

 the body-cavity, for it runs back above the gland, giving off 

 branches to it as it goes, and, after becoming attached to the 

 posterior vesicle for a short space, it dips down and unites 

 with the upper surface of the foot about the middle of its 

 length. The pedal gland, however, is many times longer 

 than this free portion of the pedal artery and is consequently 

 thrown into numerous folds and loops. In Apera sexangula 

 the gland pursues a comparatively regular zig-zag course, 

 bending alternately to the right and the left about half a 

 dozen times (PI. XIII, fig. 57). But in A. burnupi and 

 A. purcelli, and in the posterior part of the gland in the 

 remaining species, the loops are deeper and more complicated, 

 twisting about in all directions (figs. 52-56). The gland 

 attains its greatest length in A. burnupi, in which its folds 

 not only extend up the sides of the body-cavity, but even 

 curve over on to the top of some of the other organs (PI. IX, 

 fig. 30). 



The Glandular Tissue. — The pedal gland of Apera is not 

 only unusually long, it is also often exceptionally broad, as, 

 for example, in A. burnupi and in the anterior half of 

 its length in A. dimidia (PI. XIII, figs. 56, 54). In 

 A. gibbonsi and A. parva it is more slender (figs. 52, 53), 

 possibly because the great size of the odontophore in these 

 species leaves little room for the growth of any other bulky 

 organ in the anterior half of the body-cavity. 



The breadth of the gland is due to an enormous develop- 

 ment of glandular tissue on the floor and sides of its duct. 

 In Apera purcelli, A. burnupi, and A. sexangula this 

 glandular tissue extends along the whole length of the duct 

 as far as the terminal vesicle ; but it is less abundant towards 

 the posterior end and the gland becomes rather narrower 

 behind in consequence. In A. gibbonsi rubella the 



