140 EVOLUTION AND DISEASE. 
logists hold the opinion that all these appendages are 
modifications of a common type. Normally the eye- a 
stalk corresponds to the protopodite of an abdominal 
limb, consisting of a short basal and a long cylindrical 
terminal joint, the distal surface of which is covered with — 
corneal facets. In A. Milne-Edward’s Palinurus we find 
a normal ophthalmite on the right side, but the left one 
“has taken on antenniform characters.” . 
Fic. 77.—Cephalon of a Rock-lobster (Palinurus penictllatus), 
with an antenniform process growing from the inner 
aspect of the eye-stalk. (After Howes.*) 
Professor Howes points out that the corneal facets 
on the eye-stalk of decapod crustaceans do not in 
many instances surmount the whole of the free sur- 
face; frequently the outer free border is destitute of 
corneal facets, and often is swollen and well differen- 
tiated. This is so in Padinurus, and would serve to 
support the view that the facetted portion of the oph- 
=“ Proc, Zool..soc. 1889; 
