MORPHOLOGY OF MBLIBE 527 



of the ventral side. List finds three kinds of glands in the 

 foot of Tethys fimbriata Linnaens : two of these are 

 unicellular and the third is multinuclear. The unicellular 

 glands with one nucleus are located on the dorsal side of the 

 foot ; the multinuclear glands are found on the ventral side 

 of the foot. Some of the mononucleate unicellular glands 

 contain a fatty substance. The foot is covered by a layer of 

 ciliated columnar epithelium with basally placed nuclei. 

 Between these epithelial cells unicellular and multinucleated 

 glands open to the outside through an individual pore or 

 crypt. The structure of the foot of M. leonina conforms 

 very nearly to that recorded by List for Tethys. It is not, 

 however, my present intention to make a critical physiological 

 or morphological comparison of the foot in these two types. 

 The ' mehrkernige Driisen ' of List I am unable to recognize 

 in this species. PI. 30, figs. 26, 27, 28, and 29, show the relation 

 of the unicellular mucous gland to the ectoderm. These 

 glands are highly granular in structure with a central nucleus 

 (PL 30, fig. 28, Gmug, Nk). They are basophil in their staining 

 and there is a marked contrast between them and the nerve- 

 cells which are scattered all through the foot as a net. The 

 latter, however, is firmly aggregated into a pedal ganglion 

 in the posterior end of the foot (PL 30, figs. 27, Gl, 29, 

 rdgn). 



The function of the pedal glands seems to be that of secreting 

 a mucus for the purpose of aiding the animal in its progressive 

 movements when creeping on the surface of any object. This, 

 in fact, is also practised among terrestrial gasteropods, some 

 of which may use the pedal secretion to spin themselves from 

 the limb of a tree or some other plant to the ground. In the 

 Aeolidia the activity of the pedal glands is so great that 

 a few specimens (circ. l|cm. long) confined in a finger-bowl 

 for a few hours may produce a complete film of slime on the 

 surface of the water, to which the organisms adhere. 



