728 



ZOOLOGY 



SECT. 



suckers ; but it is supposed that each tentacle represents not one 

 of the arms of Sepia, but one of the suckers. The tentacles are 

 arranged in two series, an outer and an inner. The outer, which 

 are borne on an annular muscular ridge of the fore-foot, are 

 nineteen on each side in both sexes. Anteriorly this muscular 

 ridge is thickened to form a massive lobe the hood (M.) in which 

 there is a concavity for the reception of the coil of the shell. 

 The hood bears two tentacles and has the appearance of being 

 composed of the immensely developed sheaths of these, completely 

 fused together in the middle line : on each side the enlarged 

 sheaths of a second pair of tentacles are closely applied to, though 

 not completely coalescent with, the hood, being separated from the 

 latter by a narrow groove. The hood, with these two enlarged 

 sheaths, is covered with a thickened tuberculated skin, and acts 

 after the manner of an operculum for protecting the tentacles 

 and other soft parts about the head. Altogether there are 

 forty-two tentacles of this outer series, including one situated on 

 the oral and another on the aboral side of each eye. The 

 tentacles of the inner series differ strikingly in number and 

 arrangement in the two sexes. In the female there are two inner 

 lateral lobes, right and left, quite symmetrically developed, and 



each bearing twelve tentacles, and an 

 inner posterior lobe divided by a deep 

 median notch into two, each half bear- 

 ing fourteen tentacles. On the middle 

 of the oral surface of the latter, close 

 to the median notch, is an oval patch 

 raised up into numerous closely set 

 ridges. In some individuals, however, 

 the whole of this posterior lobe is re- 

 presented by a vestige (or rudiment) 

 with only slight indications of the 

 tentacles. 



In the male the inner posterior 

 lobe with its ridged organ is only 

 represented by a median posterior 

 body consisting of two oval elevations 

 each divided into a number of folds. 

 The internal lateral lobes are greatly 

 modified, four of the tentacles on 

 either the right side or the left, 

 usually the latter, being modified to 

 form a structure termed the spadix 

 (Fig. 639), which is supposed to re- 

 present the hectocotylised arm of the male Sepi'a. It has the form 

 of a large compressed cone formed by the union of the enlarged 

 sheaths of three of the tentacles. The corresponding tentacles 



V 



FIG. 630. Nautilus pompilius, 



spadix of full-grown male, seen 

 from the outer side. 1, 2, 3, 4, 

 modified tentacles; 1 , withdrawn 

 into its sheath, its position and 

 shape indicated by the dotted 

 line ; 3, the flattened tentacle 

 with the rows of minute cavities ; 

 x, patch of modified integument. 

 Two-thirds of the natural size. 

 (After Haswell.) 



