MORPHOLOGY OF THE TENTACLES OF NAUTILUS. 



803 



podium and plat3rpodium, these structures being represented in Nautilus by the mantle, 

 cephalopodium and siphonopodium respectively. 



5. The recognition of a dorsal and a ventral symphysis or lines of concrescence 

 in the cephalopodium of Nautilus. 



6. The relation of the cephalic sense-organs to the cephalopodium of Nautilus and 

 their homology with the corresponding organs in Gastropoda. 



7. The presence of an outer and an inner whorl of tentacles in the cephalopodium 

 of Nautilus in apparent correspondence with the double nature of the tentaculiferous 

 epipodium of Haliotis. 



8. The presence of the funnel-organ which according to Jatta represents a pedal gland. 



9. The position, form and relations of the capito-pedal cartilage of Nautilus. 



A word may be added by way of justification for the attempt to construct the above 

 theory in the absence of embryological evidence. The enormous size of the vitellus of 

 the egg of Nautilus renders it highly probable that the development of the tentacles and 

 funnel would be direct, it would take place in situ, and the topography of the adult would 

 be maintained in the embryo, all special embryonic events, although of the greatest 

 possible interest in themselves, being of a cenogenetic nature'. I have actually observed 

 that the inner whorl of the cephalopodium arises in a perfectly direct manner (PI. LXXX. 

 figg. 1 and 2). 



The following tabular view of the principal theories relating to the arms of Cephalo- 

 poda will at once illustrate the complexity, interest, and importance of the subject. 



' This does not refer to the development of the shell and siphuncle, which is likely to afford many 

 instructive data. Even with regard to the cephalopodium important facts might be ascertained regarding the 

 concrescence of the pleural folds. 



^ In Loligo the valve develops at a late stage as an outgrowth from the inner wall of the funnel (Brooks). 



When seen from the inside of the funnel with the flaps of the latter turned aside (cf. my PI. LXXXIII. 

 fig. 27) the free border of the valve is seen to be concentric with the anterior border of the funnel. Between 



w. VI. 105 



