G. A. DREW ON YOLDIA LIMATULA, SAY 5 



When retracted the tentacle presents a series of transverse wrinkles, 

 Fig. 6. Beneath the layer of epithelium, Fig. 8, ep., run strands of 

 longitudinal muscle fibres, 1m., imbedded in connective tissue. On the 

 side of the tentacle nearest the lobe of the mantle to which it is attached, 

 inside the layer of muscles, is a large nerve, tn., which can be easily 

 traced to the tip of the tentacle. This nerve is a branch of the posterior 

 pallial nerve. It is not given off directly opposite the base of the ten- 

 tacle, but some distance above it, and the two nerves continue along, side 

 by side, until the tentacle is reached. The appearance of the two 

 nerves lying side by side is quite like that of a ganglion, and has, 

 no doubt, been mistaken for one. On the side of the tentacle 

 opposite the nerve, also within the layer of muscles, is a more or less 

 definite blood-space, bs. 



Extension of the tentacle seems to be accomplished by forcing- 

 blood into this space. In favorable cases blood corpuscles can be 

 seen moving along it when the tentacle is being extended. If 

 considerable force is exerted in extending the tentacle, swellings, 

 Fig. 7, may occur in it. Such swellings are filled with blood and 

 disappear when the pressure is removed. When the muscles of the 

 tentacle contract, the blood is forced back and the blood-space may 

 be completely obliterated. 



The tentacles that fringe the postero-ventral margins of the 

 mantle, have, beneath their epithelium, both longitudinal and trans- 

 verse strands of muscle fibres, and generally several blood-spaces. 

 While branches of the pallial nerves have not been traced into these 

 tentacles, such branches can be traced to their bases, and there 

 can be no doubt that the tentacles are supplied by fibres from these 

 nerves. 



Each tentacle has at least one papilla and frequently there are 

 several papilla? upon its surface. In development the tentacle is pre- 

 ceded by a single sense papilla which is carried out by the growth of 

 the mantle near its base into a conspicuous projection. As this pro- 

 jection grows, other sense papillae make their appearance on its sides, 

 and the papilla at its tip may or may not retain its position. In a 

 few cases the tentacles divide or branch. This is most common with 

 the tentacles fringing the posterior expansions of the mantle, soon to 

 be described. 



Considering the origin, structure, and innervation of the siphonal 

 tentacle and the marginal tentacles, there can be but little doubt that 



