8 WALTER K. FISHER, 



lingual organ, and radula, when the animal is feeding, is illustrated 

 by Fig. 11. The portion of the palp which appears smooth in this 

 figure, is covered by columnar epithelium (Fig. E) over which is a 

 thin cuticle beset with tiny sharp points or spines. The wrinkled 

 portion of the palps (in Fig. 11) does not possess these minute points. 

 In the upper part of the palps large mucous cells are present in the 

 muscle and connective tissue (M. C Fig, E). Blood from the sub- 

 lingual artery has free access to the spaces within the palps, which 

 are undoubtedly extended or swollen by this medium. Special re- 

 tractor muscles {6 Fig. 9) are present. These are well developed 

 and extend from the interior of the palps to the posterior end of the 

 buccal cartilages. A very abundant nerve supply springs from the 

 lingual ganglia. Without any doubt there are no structures about the 

 mouth which are so highly sensory as these. 



The radula possesses no peculiar features, and its relations are 

 shown in Figs. 2, 4 and 11. The muscles manipulating it are de- 

 scribed below. On either side of the area of teeth there are chitinous 

 wing-like expansions and these seem to function chiefly for the in- 

 sertion of muscles (Fig. 16). The radula tube, just behind the buccal 

 mass, passes out of the cephalic artery in which it is encased, and 

 enters the blood sinus of the head, or head cavity, on the left side, 

 then plunges into the visceral mass, being surrounded by the visceral 

 artery. It then follows a course backward between the loops of the 

 intestine (Fig. 1), curves to the right in the lower layer of the liver, 

 then upward, and bends forward, returning to a point just above its 

 entrance to the visceral mass. Here it reenters the head cavity, and 

 ends in a little knob, attached to the anterior aorta, where it divides 

 into cephalic and pedal arteries. In Fig. 14 the arrangement of teeth 

 is shown. 



The sublingual organ hangs from under the end of the odonto- 

 phore into the subradular pocket. To all appearances it is a mere 

 fold of the epithelium, wrinkled transversely when not turgid with 

 blood. But it is really a quite definite structure, as is now well 

 known. In cross section it is triangular because of a slight longi- 

 tudinal constriction on either side, where the organ joins the dorsal 

 wall of the subradular pocket (Fig. E). Seen from the front, when 

 the creature is feeding, its relations are shown by Fig. 11. Fig, 4 

 gives an idea of its position when viewed from the side. The organ 

 is covered with a cylindrical epithelium which secretes a heavy cuticle, 

 produced into sharp teeth, forwardly directed. These tiny teeth are 



