62 Prof. J. Van der Hoeven on the Anatomy 



surface divides the hood into two lateral parts ; the upper sur- 

 face is moreover rippled with transverse furrows, which cross, 

 especially forwards, other finer furrows that run longitudinally ; 

 it is covered by many small scattered tubercles of unequal size, 

 of which the largest resemble the papilla vallatce of the human 

 tongue. Under the anterior margin of the hood is seen on each 

 side of the middle furrow, at the distance of about a centimeter, 

 a transverse incisure or aperture, from which a dark-grey ringed 

 tentacle can be protruded; these tentacles retreat within the 

 hood to about 4| centimeters. At each side of the hood lies 

 the thick external integument of the head, which is divided into 

 18 incisures*. These incisures or slips coalesce behind and 

 form, as it were, a cup ; the undermost incisures close in over 

 the funnel and are here connected by a thick margin excised 

 anteriorly. Four of these slips lie more outward and backward ; 

 the rest form, as it were, a verticilliLS ; on the inner surface all 

 these sHps form with the hood a connected whole, which, as an 

 external covering, surrounds circularly the membranous oral 

 mass in which the jaws are situated. The first slip that suc- 

 ceeds to the hood on each side, closes immediately upon it and 

 forms above and forwards a border, as it were, round the hood, 

 of the same colour and surface as itself; the remaining slips lie 

 on the side and downwards, and are not visible in the aperture 

 of the shell, by which they are covered at the side ; they are of 

 a paler colour and present ripples indeed, but no tubercles or 

 papillse. In each of the slips a ringed tentacle is contained, of 

 the same colour as the two tentacles of the hood. These tenta- 

 cles project, sometimes more, sometimes less, from the apertures 

 of the slips, in which respect great variety prevails in difi*erent 

 specimens; they can, however, be retracted entirely within the 

 slips. Owen has correctly remarked that the hood is formed by 

 the coalescence of the two uppermost slips of this encircling 

 membr-anous covering of the mouth. 



In these parts there is no remarkable difference from those of 

 the females which have been examined hitherto ; at least the 

 difference does not consist in the number of the tentaculiferous 

 slips. But it seems, on the other hand, that a variety in this 

 respect may occur which is independent of sex ; for Owen 

 counted 19 slips on each side without the hood, in the specimen 

 which he investigated. Eighteen however appears to be here 

 the normal number, which I observed both in male and female 

 specimens, and which Valenciennes found in his specimen also. 

 But it seems to me not improbable that a sexual difference does 

 exist in the form of the hood, and that with the same mean 



* In one specimen 1 found on the right side only 17- 



