84 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



perfect series of fibrillse, whose extension in all three directions is sufficient 

 to receive the whole of any image formed by the corneal lens. The lack 

 of focal accommodation in the lens is balanced by the depth of the retini- 

 dium. The theory of vision is discussed in some detail. 



An interesting survey of other groups is given, showing how the above 

 view of the structure of the molluscan and arthropod eye unifies that of all 

 the groups. Another chapter is devoted to a development of the idea of a 

 " Funktionswechsel " in the development of sense-organs, and especially 

 eyes which were, according to Patten, not primitively perceptive, but 

 absorptive of solar energy, heliophacjous. Lastly, we repeat the author's 

 classification of eyes : — 



Ojimatidia. 



A. Chromatophores;(Ccelenterates (?) 



C 



(modified 

 ommatidia) 



B. Isolated 



ommatidia ; 



/'A. Ommatidial 

 tracts ; 



B. Pseudo- 



Icnticulatc 





Molluscs. 

 ( Crustacea (?) 



[(universal ?) 



(retinidial cuticula, fliin ; "I ,-^t ,, 

 [ no rods devfloped / ^ 



usca). 



fommatidial tracts, non-invaginatc,, 



I or but slightly so; rods form a 1 4)-ca and 



j lens-shaped, unprotected pro-| Ccelentcrates. 



I tuberance. ■' 



C. Invagiiiate 



(a) retincnm ;( 



f ("optic caps or 



I vesicles ; corneal 



(1) primary <cutiL'ula forms a 

 I vitreous body ± 

 Iprimary lens 



I optic vesicles ; 

 triploblastic ; 

 vitreous body ± 

 primary * or 

 secondary lenses 



! optic vesicles ; anterior wall 

 forms the retina ; triploblastic ; 

 cellular lens 



ICoolenterates, 

 I Molluscs, 

 1 Worms. 



I Arthropod- 

 ( ocelli. 

 iStemma. 



\Pecten and 

 (Vertebrates. 



(c) ommateum ; 



f optic vesicles; cuticular lens, ^ .^ ' 



I Limulus. 



\ single and secondary 



D. Evaginate ; 

 ommateum, 



(1) monoblastic ; 



(2) diploblastic; 



Jcorneal cuticula present, ^Arca, 



\ but no lens is formed. ] Pectunculus. 



modified optic vesicle ; 

 corneal cuticula present, 

 forming no lens or 

 many. 



1 Compound 

 ( eye of 

 j Insects and 

 I Crustacea. 



Development of Compound Eye of Crangon.t — Dr. J. S. Kingsley gives 

 a preliminary notice of his investigations into the development of the 

 compound eye of Crangon, in which it is shown to arise from a single 



• A primary cuticular lens is one formed by the corneal cuticula within the optic 

 vesicle; a secondary one is formed by the cuticula of the hypodermis overlying the 

 optic vesicle. 



t Zool. Anzeig., ix. (1886) pp. 507-COO. 



