178 



ORGANS OF TOUCH 



CHAP. 



(^Grlandina^ Aerope^ compare Fig. 21, p. 54) these palpae are of 

 great size, and curl upwards like an enormous pair of moustaches. 



Fig. 81.— Cypi'aea tnoneta L., showing tentaciilae at 

 edge of mantle, which partly envelops the shell : 

 Si, siphon; M, M, mantle; F, foot; T', tenta- 

 culae at edge of mantle. (After Quoy and Gai- 

 mard.) x §. 



Fig. 82. — Monodonta canali- 

 fera Lam., New Ireland, 

 showing mantle lobes. 

 (After Quoy and Gai- 

 mard.) 



When a Grlandina seizes its prey, the palpae (see Fig. 83) 

 appear to enfold it and draw it in towards the mouth. 



It is in the Opisthobranchiata that the organs of touch 

 attain their maximum development. Many of this group are 

 shell-less or possess a small internal shell, and accordingly, in 

 the absence of this special form of defence, a multiplied sense 

 of touch is probably of great service. Thus 

 we find, besides the ordinary cephalic tentacles, 

 clusters or crowns of the same above the head 

 of many Nudibranchiata, with lobe-like pro- 

 longations of the integument, and tentacular 

 processes in the neighbourhood of, or surround- 



FiG. 83. — Glandina . ^, , , . ^, ^. ►o i o<\ 



seizing its prey, n^g the branchiae (see J^igs. oo and o4), or 

 with buccal papii- even proiecting from the whole upper surface 



lae turned back. „ , , '' ^ .^. _ ^. 



■ (Strebei.) of the body (Fig. 5, C). 



In the Pelecypoda, the chief organs of 

 touch are the foot, which is always remarkably sensitive, espe- 

 cially towards its point, the labial palps on each side of the 

 mouth, and the siphons. In certain cases the mantle border is 

 prolonged into a series of threads or filaments. These are par- 

 ticularly noticeable in Pecten, Lepton^ and Lima (Fig. 85), the 

 mantle lobes of the common L. Mans of our own coasts being 

 very numerous, and of a bright orange colour. In many genera 

 — e.g. Uyiio^ Mactra — this sensibility to touch appears to be 

 shared by the whole mantle border, although it is not furnished 

 with any special fringing. The ' arms ' of the Cephalopoda 



