EYE OF CEPHALOPODA 



I8 



which line the interior of the depression, and which communicate 



directly with the hranches of the optic nerve, there being no 



iris (ir lens. This type of eye, 



it will be observed, corresponds 



exactly with that which occurs 



in l\(feUa. It appears also to 



correspond t»» a stage in the 



development of eyes in the 



Diliranchiata (e.g. Octopus, Sejna, 



Loligu). Lankester lias shown ^ 



that in Zolif/o the eye first 



appears as a ridge, enclosing an 



oval area in the integument. 



By degrees the walls of this 



area close in, and eventually 



join, enclosing the retinal cells 



within the chamber in which 



the lens is afterwards developed !''«• ^a- -Three stages in the develop- 



^ luent of the eye oi Loligo ; r, r, ridge, 



(Fig. 89). It thus appears that 

 in some cases the development 

 of the eye is arrested at a point 

 which in other cases only forms 

 a temporary stage towards a higher type of organisation. 



The developed eye in the dibranchiate Cephalopods consists 

 of a transparent cornea, which may or may not be closed over 



enclosing p.o.c, primitive optic cham- 

 ber ; or, orifice between the closing 

 ridges ; s.o.c, secondary optic chamber ; 

 ci, ci, ciliary body ; /, rudimentary 

 lens ; E, retina. (After Lankester.) 



I' arc 



Fig. 90. — Eye in 

 A, Loligo; B, He- 

 lix or Limax; C, 

 Kautilus : a.o.c, 

 anterior optic 



chamber ; c, cor- 

 nea ; int. integu- 

 ment ; ir, iris ; I, 

 lens ; I', external 

 portion of lens ; 

 ojj.n, optic nerve ; 

 o/j.(/, optic gang- 

 lion ; p.o.c, poste- 

 rior oiDtic cham- 

 ber ; r, retina. 

 (After Grenacher.) 



the front, of the lens. I^ehind the cornea is ;i narrow chamber 

 (the ;tnterior optic chamber) wliich is continued for three parts 



1 Quart. Jourii. Min: Sc. X.S. xv. p. 37. 



