24 PROCEEDINGS OF THE AMERICAN ACADEMY 



III. 



STUDIES FROM THE NEWPORT MARINE LABORATORY. 



XXI. — A PRELIMINARY ACCOUNT OF THE DEVEL- 

 OPMENT AND HISTOLOGY OF THE EYES IN THE 

 LOBSTER. 



By G. II. Parker. 



Presented by Alexander Agassiz, October 10, 1888. 



The following is a brief statement of the results obtained frotn study- 

 ing the development and histology of the eyes in lobsters. The method 

 in which the optic nerve appears to terminate is so exceptional, that, 

 before making a final publication on this subject, it seems desirable to 

 seek confirmation in the structure of the eyes in other Crustacea. As 

 this will delay the appearance of the paper, and since iu other direc- 

 tions definite conclusions have been reached, it seems advisable to 

 publish now an account of my present conclusions. 



The first indication of the optic apparatus in the young lobster is a 

 pair of ectodermic thickenings on either side, and slightly in front of 

 where the mouth is to appear. The superficial part of each of these 

 thickenings gives rise to the retina, and the deep part to the optic 

 ganglion. The ganglionic portion is cut off from the retinal portion 

 by the ingrowth of the basement membrane. In certain regions, how- 

 ever, the basement membrane does not cut the connection between the 

 retina and ganglion. These primitive connections persist in the adult 

 as optic nerve fibres. 



In the eye of an adult lobster each ommatidium consists of at least 

 sixteen cells. Directly under each corneal facet are found two flat 

 lentigeuous cells (corneal hypodermis). Under these are four retino- 

 phoroe, one for each angle of the corneal facet. The retinophora? 

 are extremely elongated, and extend from the deep face of the corneal 

 hypodermis to the basement membrane. From the corneal hypoder- 

 mis to the spindle the four retinophora? are closely applied to one 

 another. At the distal end of the spindle they separate, passing 

 around that structure as fibres. As they approach the basement 

 membrane they converge slightly, and terminate on the retinal surface 



