No. 471] AXATOMY or .\< .\IJ:.\ T hST CD/NA US 179 



usually (Hstin-uisluMl fn,in the Patelii.la". \Vl.iI,> tii<" family to 

 which a limprt heloiios may often he thus ivc(.u-.ii/,-<l. th<- t^nwrii 



mal to the rocks on which it lives. 'i"he .)iua!i is (oiiii)..s,-<| . liielly 

 of muscle fibers most of which run from the >hell ventialwanl. 

 spreading both laterally and toward the median line. A few fibers, 

 however, are parallel with the sole and run either lenjrthwise or 

 transversely. The fibers are iml)edded in comiective tissue and 

 are entirely \vantin<; near the margin of the foot, which is com- 

 posed mainly of connective tissue excavated l)y lar<re blood siinises 

 and is therefore extremely flexil)le. 'Certain mariiiiial nnicenular 

 glands, whose secretion may aid the foot in clintzinu-. are (hvsci ibed, 

 together witli the epithelium in general, under th(- topic hilcfin- 

 merif. Just in front of the foot appears a ventral {)rol()iigati()n of 

 the head, the muzzle; it bears on its tip the small circular mouth 

 surrounded hy the simple frill-like lip, which is characteristic of 

 the subgenus Collisella. In a specimen which has been narcotized 

 with chloretone the moutli is usually dilated enoui:h to show the 

 yellowish brown inner lij). Fiu'. 1 < and in a fresh one it> coniiinial 

 opening and closing permits a good view of the radnla. wliicli has 

 a constant licking motion. It has been suiiu'ested by Davn and 

 Fleure (:03, p. 49) that this movement serves to keep in nioiion 

 the blood in the cireumodontophoral sinus and thu- ivinforees 

 the feeble ventricular muscles. 



At the sides of the muzzle appear a pair of Ion- and \vv\ con- 

 tractile tentacles; they are borne on tli(> po^terioi- part of the head 



