E. W. BERGER ON THE CUBOMEDUS^E. 43 



of it remains. As concerns most of my series I could not well 

 determine which were from younger and which from older 

 individuals, yet, several series of quite small (5 mm.) and therefore 

 young animals, in which the eyes were so small that the lenses were 

 compassed into less than half a dozen sections, the cellular structure 

 of the lens was very evident. 



The external cells of the lens form a spherical shell (both complex 

 eyes) which, in section, shows as a hollow ring (Figs. 7, 13). The 

 thicker ends of these cells lie at the inner (toward the capsule) half 

 of the sphere and the cells taper toward the corneal surface, dove- 

 tailing laterally with their immediate neighbors as also distally with 

 those from the opposite side of the sphere. The thicker inner ends 

 of the cells contain the large nuclei with nucleoli. At a point (*Figs. 7 

 and 13) on the inner (next the capsule) surface of the lens the cells only 

 approximate each other and thus leave a place which is easily 

 broken through, as is shown by portions (drops, probably representing 

 cells or portions of cells) of the mass within the lens becoming 

 squeezed out into the substance of the capsule and the vitreous body, 

 and found occasionally also among the cells of the retina. A 

 considerable portion of the inside of the lens may be found thus 

 squeezed out, and its path can often be traced. This phenomenon is 

 evidently brought about by a contraction of the shell of the lens 

 during fixation and before the inside of the lens has become 

 hardened. 



In origin the lens is evidently ectodermal, originating from an 

 ectodermal invagination which becomes pinched off as a hollow 

 sphere, the outer (i. e. next the cornea) half of which becomes the 

 lens, the inner half the retina (i. e. vitreous body plus the so called 

 retina). (See Retina.) The transition from retinal to lens cells is 

 quite readily made out at the lower side of Fig. 7, but the corres- 

 ponding structure on the upper left side is not so manifest. It is 

 further evident that the lens is again an . invagination into this 

 sphere, and the point at which the lens cells approximate (where the 

 central mass of the lens may be squeezed out as above described) 

 represents the place of pinching off of the original lens-retina sphere. 

 It appears, then, that the lens is formed in the lens-retina sphere in 

 the following manner : The cells of the secondary invagination 

 going to form the lens begin to lengthen distally (i. e. toward the 

 cornea) during their invagination to form a hollow sphere, at the 



