LABIAL APPENDAGES (S. S. 437) 135 



When the posterior portion of the tail is cylindroid, the terminus is 

 usually almost imperceptibly expanded, and the spinneret is then some- 

 what differently developed, and is usually armed 

 with obscure, innervated, submedian papillae or 

 setae. 



Head 



Lips. In the view usually obtained the six lips 

 appear to be more or less confluent, and if it were 

 not for their papillae it would be difficult to count 

 them ; but when thrown apart, an attitude in which, x 1000 

 however, they are seldom seen, they are more easily ,, 



J J J ric. 5* opinncret ox 



counted, since in this attitude the refractive "cerat- '"Ss^whos*' contrac- 

 inous" internal elements of the lips are separated Jon ^open s w the se spinneret 

 from each other and more readily distinguishable, as shown in figure 1. 

 When closed, these six, broad, flat lips meet together in such a way that 

 the star-shaped mouth opening usually lies in a slightly depressed area on 

 the middle of the front of the head. In some species the inner walls of 

 the lips are strongly "ceratinized," and may be developed into six rather 

 definite, retrorse, subacute points, which, in assaults on other animals, 

 serve as grappling hooks, and act in opposition to the dorsal tooth of the 

 pharynx. 



Labial papilla. Each lip is supplied with at least two, usually more or 

 less conical, innervated papillae; one on the outer margin and somewhat 

 outward pointing, the other situated about half way between the outer 

 papilla and the centre of the head, and forward-pointing. The front of 

 the head therefore presents two circlets of papillae, one on its outer mar- 

 gin, and one more closely surrounding the mouth-opening, as shown in 

 figures 1 and 4, and many others. These papillae may be so flat as to 

 play no conspicuous part in the external conformation of the head, or 

 they may be conical and raised, so as to give to the front of the head a 

 more or less angular contour. The papillae are slightly mobile, and hence 

 vary somewhat in appearance at different times on the same specimen, a 

 matter depending on the attitude of the lips. Drowned specimens with 

 relaxed lips present a slightly different appearance from those that have 

 been fixed for examination by means of chemicals. 



Some of the innervations that frequently occur on the head near the 

 lips may have special functions. Structurally they are sometimes indis- 

 tinguishable from the subordinate labial papillae. The species figures 

 show the location of some of these innervations. One pair of them is 

 very near the amphids the only nerves so far observed to be definitely 

 associated with the amphids. These particular papillae are so uniform in 

 their' occurrence that it seems likely they have a special function, con- 

 nected with the use of the amphids. 



