Slonaker, Eye of the Mole. 343 



conditions found in the young at birth are very similar to those 

 here represented. By careful examination a single layer of cells 

 may be seen extending over the anterior surface. These cells 

 no doubt correspond to the layer normally present in the de- 

 velopment of all vertebrate eyes. These cells are very much 

 smaller than those composing the posterior and larger part of 

 the lens. One can safely say that such a structure could not 

 function as a normal lens. 



In the development of the lens of the European mole 

 Kohl finds that it proceeds in a normal manner, that at birth 

 the cells of the posterior part of the lens capsule has elongated 

 and almost completely filled the capsule. These cells appear 

 at this stage as typical elongated lens cells with very distinct 

 and large nuclei. I have not succeeded in finding such an 

 arrangement in the young of the common mole even though 

 sections were made in various planes of the eye. There is, 

 therefore, a very great difference in these two species at birth. 

 The lens of the common mole seems much more degenerate. 

 Owing to the lack of material with which to study the embry- 

 onic stages, I am unable to say just how this degenerate con- 

 dition has been reached. Two theories may be given : 

 (l) after the lens has developed in a normal way the cells have 

 been reduced to the condition found in Fig. 22 ; or, and this 

 seems to me the most probable, (2) instead of the cells of the 

 posterior part of the capsule elongating and developing into 

 typical lens cells, they have simply increased in size and num- 

 ber. At a later date I trust I may be able to procure material 

 and to clear up this matter. Ritter (5) favors the latter 

 hypothesis. 



The choroid and pigment layers are so densely pigmented 

 that it is almost impossible to distinguish the boundary between 

 them. These layers extend forward to the lens, where they 

 end in the region of the ciliary muscles. Sometimes a slight 

 projection can be perceived extending forward (Fig. 7) which 

 is all that is to be seen of the iris. The iris at this age is gen- 

 erally absent and the pupil is as large in diameter as the trans- 

 verse diameter of the lens. This condition also indicates that 



