2 CARL VON HESS 



If one views a fresh alciopid eye from in front, the surface 

 surrounding the lens is seen to be threaded over with numerous 

 fine silvery shining stripes, which have hitherto been mistakenly 

 interpreted as muscles (Hesse). In fact these are structures 

 which, like an iris, obstruct the passage of diffuse light into 

 the eye; besides this, they make the eyes which are turned 

 forward and downward, as invisible as possible to an enemy 

 coming from below. They thus have the same effect as that 

 which I some time ago proved to be the case with the silver 

 sheen of fish. 



Just below the lens there is a spot in the very soft eye-wall 

 which, one may observe, contracts when the eye is stimulated; 

 all the other portions of the tegument remain motionless. The 

 lens, when stimulated, moves forward perceptibly, it approaches 

 the cornea, as one may perceive most readily by looking at the eye 

 in profile. Herewith is proved that the alciopids have an active 

 near accommodation; for, by the above-mentioned contraction 

 the distance between the lens and the retina is increased, while 

 the lens remains unchanged in form. The way in which the 

 change in the location of the lens is brought about is most inter- 

 esting: The alciopids are distinguished from all other animals 

 with otherwise similarly constructed eyes, by possessing a double 

 vitreous body. Directly back of the lens we find a viscous 

 fluid which is distinctly separated from the posterior space of 

 the vitreous body and adheres closely to the w T alls of the eye 

 on all sides. At the lowest point of this front part of the vit- 

 reous body the latter displays a curious ampulliform knob which 

 is connected with the eye-water space by a canal and was form- 

 erly interpreted as an auditory sac by zoologists, and at present 

 is supposed to be a gland belonging to the vitreous body for the 

 secretion of its substance. My experiments show the real use 

 of this protuberance. It occupies exactly the spot in the eye- 

 wall in which alone contractile elements are found; the muscles, 

 contracted, press the lump together like a rubber bulb filled with 

 liquid, thus forcing a part of its contents into the eye, and 

 slightly pushing forward the lens which rests in a bowl-like 

 groove in the front surface of the vitreous body. 



This is the second accommodative process among the inver- 

 tebrates with which we have become acquainted ; the mechanism 

 differs entirely from that which I have proved Cephalopods to 



