102 K. KI8HIX0UYE. 



pears, niid the epiblnstic tliickeuing above the lateral \esic]e, which 

 latter is by this time separated from the general epibla.st becomes flat. 



A\ lieu the reversion of the emljryo is almost over, a- differentia- 

 tion occurs among the nuclei of the epil3lastic thickening. At three 

 places in the thickening, luiclei become a little larger, and stain slightly 

 less than those which are found elsewhere, ajid wdiich are pressed 

 together and are of a long ellipsoidal shape (fig. 1j). 



These three groups of larger nuclei form the retinal portion of 

 tlie three lateral eyes. They are spindle-shaped or rather wedge- 

 öhaped, narrower towards the exterior surface. Later tliey are separated 

 from the surrouiiding nuclei at the narrower end l)y a ring-like furrow, 

 peculiar to tlie lateral eyes, and the surrounding nuclei grow and ineet 

 together o\er the retinal |)ortion, forming a layer of cells — the 

 ^itreous body. 



The lateral eyes receive tlieir ncr\es from a portion of the brain, 

 formed ])y the lateral vesicle. Thus the latter is the optic ganglion, 

 formed from an invagination, independently of the semicircular 

 cephalic groo^'e wdiich gives rise to the brain proper. 



The common epif)lastic thickening of the lateral eyes of spiders is 

 most probably homologous with the e]>iblastic thickening of the 

 lateral compound eyes oi' Liiiiuln.^, as its position is just the same :ind 

 the invagination is similarly produced in both cases. Then, are the 

 peculiar groups of larger nuclei of spiders homologous Avith the 

 tmimatidia of Jy///i/f///.s / 1 am inclined to believe that such is the case 

 and that fli<' lalrral riics of .spiders are se/Kirated, ('tilargril. au(J modified 

 (jmiiKttidia of a coDipinuid eye of tlie iv ancestor. 



In PI. W, illustrating Parker's ])aper " 'Ilie Eyes in Scorpions," 

 we distinctly see that all tlie lateral eyes of the scor])ion tilso arise from a 

 Ci)ninion thickening o!' tlie epiljlast. Thus we see that the occurrence of 

 this interesting plienomenon is not confined to spiders but is found in 



