< HORIO-ALLAXTOIC GRAFTS. ~ - 



With the experiments made from the eye primordium of the 

 forty-eight-hour embryo, greater difficulties with the elmination 

 of the surrounding tissue began to appear. It is practically 

 impossible to isolate absolutely the optic cup of this stage from 

 the surrounding mesenchyme without injuring the cup in some 

 w.iy. The optic cup can In- dissected out with little difficulty, 

 but in every case tin- re- may be seen a fur-like border of the 

 mesenchymal cell- attached to its surface. After a few , it tempts 

 to remo\e tin-, it was con-idered to be useless, for the manipula- 

 tion injured the rup in c\ery case. On thi- account, when a 

 tr. m-plantation of ilie optic cup is spoken of. it means that the 

 optic cup t-r with the immediate me-cnchyme w.i- taken. 



Attempt-- were made 1.- in the experiment- with the thirty- 



hour embryo-, t.. n nio\e the lens primordium from the optic 

 cup. It v. 'ii found that, though thi- i- po->ible, tin 



; of me.haiiic.il injury involved. Such experiments 

 were therefore omitted. Since the sixty-hour "eye" i- in much 

 the same <"iidition, the -.line difficulties wen- experienced \\ith 

 it, but it \\a- not con-idered necessary to perform main- ex| 

 inn nt- \\ith the material I nun this age, for even at thirt\--ix 

 hour- of incubation. : s of the optic primordium po- 



complete \> \\emf independent self-differentiation. 



In the grafts obtained from the foveola of the t \\ent\--four hour 

 embr\o, there i- much \ariability in growth and differentiation. 

 Thi- -eem- to be due to t' that there i- a < eitain amount of 



cm -hi n- ini he n-mi\ al of tin- ti--ue, thedi- :/atii>n prodi: 



bv tlii- nu-( hanical factor incn-a-ini; a- the >i/e of the operated 



pan d. In one of the. there is a primary differentia- 



tion into tapetal cell- \\hii-h contain pigment granule-, and 

 retina-forming cells. Man\- of the graft- >ln>\v iu-r\-ou- ti--ue 

 but it is not -ulticicntly different iati-il to warrant any po-itive 

 r.tatement a- (<> it- iiatun-. There i- much other ti ue tran-- 

 planted with the optic primordium of thi- age. In One of [lie 

 ;jralt- \\ell defined ^an^lion cell- are present. In no case, ho\v- 

 ever, does any eye j;raft of thi- a;^e -how more than the primary 

 differentiation into pi^mcnted ta|>etal cells and implemented 

 retina-forming cell-. 



The Drafts of the optic \e-icle pin- the lens ectoderm of the 



