l62 



THE PINEAL ORGAN 



ant os 



cten 



pt neph 

 I vise ap 



Fig. 119 



Nautilus pompilius, showing the Central Apertures of the Eyes. (After 

 Willey, from Parker and Haswell's Textbook of Zoology.) 



The flattened external surface of the eye is bounded by a slightly raised rim, 

 which extends round the posterior half of its margin. From this a narrow 

 groove extends inwards to the central opening, which has some resemblance 

 to the choroidal fissure of the lateral vertebrate eye. The eye of Nautilus 

 is, however, extremely simple, consisting of an open cup, the cavity of which 

 is filled with sea-water. It has neither lens, iris, nor vitreous humour. 

 The rods or inner refractile segments of the cells are directed towards the 

 light and the nerve fibres originate from the opposite end. The interior of 

 the mantle cavity is exposed, the postero-ventral wall having been reflected. 



oral left renal aperture. 



a. I. neph. 



an. : anus. 



ant. os. : right oral osphradium 

 (olfactory organ). 



cten. : ctenidia or branchial organs. 



ey. : eye. 



f. : funnel. 



gr. : groove leading to central aper- 

 ture of eye. 



/. 6 . ap. : bristle passed into left re- 

 productive aperture. 



/. vise. ap. : left viscero-pericardial 

 aperture. 



pen. : penis. 



pt. neph. : aboral left renal aperture. 



p. os. : aboral osphradia. 



sp. s. : spermatophoral sac. 



v.n. : visceral nerves. 



