366 



INVEETEBEATA 



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 

 Sepia. 



By far the most 

 complicated organ in 

 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 



Fig. 298.— Two early stages in the development of the Segment of the lens 



eye of Loligo vulgaris seen in trausverse section, begins to be formed 



(After Lankester. from B.lfour.) jj. ^^^^ appears aS a 



00, eye-o.,p;r, rudiment of retin.-,. ^j^-^ CUticlc Spreading 



Fig. 299. — Sectious through tlie 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 epitheliale ; c.ep^, 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 ; ir, iris ; 



l.f, lens fibres. 



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

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



