56 BULLETIN OF THE 



Graber ('79, pp. 84, 85, Figg. 13, 14) found that in the median eyes 

 of Buthus there was left, after the action of caustic potash had made 

 the central portions of the sections paler, a rose-colored granular rim or 

 marginal zone, and that in this zone were to be seen a few, mostly in- 

 distinct, nuclei and markings perpendicular to the sclera, which together 

 might serve at first sight to suggest the presence of a tall cylindrical 

 epithelial sclera-matrix. This view Graber definitely puts aside, how- 

 ever, and concludes that the appearance is due to the oblique direction 

 of the section, the apparent epithelium being only the cut-ofi" (anterior) 

 ends of " Retinaschlauche." But inasmuch as there are no other sub- 

 cuticular (subscleral) structures, these " retinal sacs " have assumed, in 

 his opinion, notv/ithstanding their other functions, the rote of matrix- 

 cells. 



Even without our present knowledge of the manner in which similar 

 eyes arise, this interpretation would be unsatisfactory, because the mar- 

 ginal zone is most sharply marked off from the retina in the posterior half 

 of the ball of the eye, and it would be difficult to imagine the course of 

 retinal cells which in this region could be so cut as to give rise to the 

 appearance figured. But I do not doubt the accuracy of the figure in 

 question (Graber's Fig. 14), and believe that its interpretation becomes 

 easy when considered iii connection with the probable origin of the re- 

 tina. If the median eye in Buthus was formed by an involution with 

 inversion of the retina, Graber's " Matrixzone " would be the posterior 

 layer of that infolding, and its gradually merging into the retinal layer 

 in the anterior half of the ball of the eye would be entirely parallel to 

 what occurs in the formation of the " pre-nuclear " eyes in spiders. 



Lankester and Bourne ('83) have also had under consideration this 

 pigment- and matrix-zone of Graber, and have arrived at conclusions 

 which are entirely new. It will be most satisfactory to quote their own 

 words upon what they call " intrusive pigmentary connective tissue : " 

 " The structures which we consider as intrusive connective tissue in the 

 central eyes of the Scorpion may be compared to the interneural cells 

 of the lateral eyes. Like these, they are pigmentiferous, and serve 

 to fill up the spaces between the several nerve-end cells and between 

 these and the ommateal capsule. But whilst we regard the interneural 

 cells as ectodermal in origin, . . . we find reasons for considering the 

 intracapsular pigmentary connective tissue of the central eyes of Scor- 

 pions as derived from mesoblast, and of the nature of connective tissue. 



" We have not embryological evidence for this conclusion, and depend 

 entirely upon the branching, inosculating character of the pigmentary 



