INVERTEBEATA 



CHAP. 



reacquire their cavities, and then the kidneys become fused together 

 in the mid- ventral line ; this fusion is characteristic of Loligo, and 



does not occur in 

 A 



the most 

 organ in 



FIG. 298. Two early stages in the development of the 

 eye of Loligo vulgaris seen in transverse section. 

 (After Lankester, from Balfour. ) 



oc, eye-cup ; r, rudiment of retina. 



Sepia. 



By far 

 complicated 



the Cephalopod is the 

 eye, the general features 

 of the development of 

 which have already been 

 described. Some details 

 may now be added. As 

 soon as the primary 

 eye pit closes the inner 

 segment of the lens 

 begins to be formed. 

 It first appears as a 

 thin cuticle spreading 



1. 



FIG. 299. Sections through the developing eyes of young cuttle-fish to show the 



development of the lens. (After Faussek.) 



A, Section through the eye of Loligo vulgaris. B, Section through the eye of Sepia officinalis. c.ep, 

 large cells of the corpus epithcliale ; c.epi, small cells of the periphery of the corpus epitheliale which 

 grow over the larger cells and secrete the fibres of the lens ; i.l, inner segment of the lens ; it; iris ; 

 l.f, lens fibres. 



over a considerable portion of the inner surface of the closed eye- 

 sac, but it becomes thickened at one point in the centre, and 



