20 



the male, are stored in this arm, which, when packed with 

 them, becomes detached and in some way enters the mantle 

 cavity of the female. The arm of Eledone, however, is 

 less specialised and not autotoinous, and the chief 

 modification is at the tip, as in Octopus. Probably then 

 the tip of this arm is inserted in the terminal part of the 

 oviduct of the female, after the manner actually watched 

 and figured by Racovitza in the case of Octopus. The 

 hectocotylised arm of Eledone is somewhat shorter than 

 the others — about 13 mm. less in the small specimen 

 examined of E. aldrovandi. Examining the ventral sur- 

 face, it may be seen that the third right arm counting 

 ventrally from the dorsal pair — bears a groove on its 

 ventral aspect (IV, gr.). This is formed by a narrow fold 

 of skin, and runs from the base to the tip of the arm, 

 where the groove is enlarged to form an oval depression 

 on the oral surface of the arm tip (IV, depr.). Moreover, 

 the other seven arms of the genus Eledone are somewhat 

 modified in the male. The suckers at the tip are set more 

 closely together than in the female, and are shallower 

 (I\ b, S). The sixth and seventh suckers from the tip 

 have practically no cavity at all, and the remaining ones 

 are represented by tiny flat pads (IA 7 b, P), 



(B) Visceral dome.— This is the name given to the 

 mass formed by the principal viscera of the body. 

 Externally it is enclosed by the thick muscular mantle. 

 It is oval in shape, being longer than it is broad, and 

 bluntly rounded posteriorly. Anteriorly the visceral 

 dome is marked off from the head bv a slight constriction 

 or neck. The dorsal surface is more convex than the 

 ventral, and lies uppermost during creeping and 

 swimming. As the shell is greatly reduced in Eledone, 

 the visceral dome is unprotected save by the skin and 

 muscular mantle. 



