THE EYE. 397 



adduced, and the more so, because, as I have shown (§ 24), 

 all the subcutaneous connective tissue of the foetus is at one 

 time perfectly gelatinous, and, like the enamel organ which 

 also belongs to the same tissue in specie, strikingly resembles 

 the vitreous body in aspect and consistence. 



Concerning the histological development of the eyes, the 

 following only need be remarked. At an early period they 

 consist in all their parts of formative cells of uniform size, 

 which, in process of time, are metamorphosed into the various 

 tissues. In the fibrous coat, in the second and third month, 

 the cells are developed, in the mode already described 

 (§ 24), into connective tissue, and at the same time the 

 distinction is set up between the cornea and sclerotic, which 

 are at first, externally, exactly alike, and constitute only a single 

 membrane. In the uvea the cells are for the most part 

 employed in the formation of vessels ; another portion goes to 

 the formation of the inner and outer pigment-layers, pigment- 

 granules being deposited in them at the commencement of the 

 third month, whilst another is transformed into muscles, 

 nerves, the epitkelia and connective tissue of these membranes. 

 The development of the nerve-cells and of the so-termed 

 u granules" from embryonic cells, may be readily traced. I 

 have observed the same thing also with respect to the " cones;" 

 and I think that, in the Frog, it may be assumed with respect 

 to the "rods" likewise, that they are nothing but elongated 

 cells ; whilst in the Mammalia, the formation of the " rods," 

 and of the nerve-fibres themselves, has not yet been traced. 

 The lens, lastly, is originally composed entirely of cells, which, 

 in course of time, are transformed into the tubes. The precise 

 nature of the processes attending these changes has not yet 

 been investigated, although I agree with H. Meyer in the 

 conclusion, that since the tubes, both in the foetus and child, 

 present only a single nucleus, each of them is developed 

 out of a single cell. These nuclei, taken as a whole, con- 

 stitute a thin layer, extending from the borders of the lens, 

 through the middle of its anterior half, and slightly convex in 

 front (" nuclear zone," Meyer) ; the nuclei being smaller in the 

 interior portions, and as it were in progress of solution, whence 

 it may certainly be concluded that the lens increases by the 

 apposition of thin layers from without. The formative cells of 



