32 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
“possibly in Copepods.” ‘The essential point is that the retina is 
separated from the hypodermis, but not by the formation of an optic 
pocket. ‘The method of separation in Amphipods is by means of a 
membrane, the corneo-conal membrane, which is, in Parker’s opinion, 
composed of two layers, one formed by the retina, the other by the 
hypodermis. ‘The two portions of the corneo-conal membrane are 
seen to be separate at the edge of the retina, one being the basement 
membrane of the hypodermis, the other forming the capsular mem- 
brane, which envelopes the retina and is finally reflected over the optic 
nerve. In Gammarus the corneo-conal and capsular membrane 
completely enclose the retina and separate it from all other tissues 
with the exception of the optic nerve. 
In Copepoda, too, the retina is separate from the hypodermis, and 
in Argulus the separation is made more extensive by an intervening 
blood space. The retina in the Eucopepoda as represented by the 
Pontellidae and Corycaeidae is apparently not continuous with the 
hypodermis, but Parker (91, p. 59) states that it is difficult to decide 
to which of the three types the retina in Copepoda belongs. “.... If 
the lateral eyes in Copepods are not representatives of a fourth type, 
essentially different from the three already described, they must be 
considered members of the third retinal type.” Hesse (:02) has 
grouped the eyes of many invertebrates in a way similar ,to that em- 
ployed by Parker (91), but the work of the former writer will be 
referred to more extensively later. 
It may perhaps be questioned whether the median or “nauplius”’ 
eve of such Copepoda as Eucalanus, Cyclops or Diaptomus, may be 
justly compared with the eyes of a distinctly higher type, which are 
found in other Crustacea. But the relation of the parts of the eye to 
the ectoderm in Eucalanus are striking, and exactly along the lines 
marked out by Parker (91) in his treatment of the compound eyes 
in Crustaceans. It seems to me, therefore, that it is worth while to 
consider the matter, since it is important in a discussion of the phy- 
logeny of the median eye. 
Nothing is known concerning the ultimate relation of the median 
eye to the hypodermis, or other membranes, except that it is developed 
from ectoderm (Grobben, 781; Urbanowicz, 781; Claus, ’91, p. 259), 
as in all other Crustacea. Claus (’91, p. 260) treats of the enveloping 
membranes in the following words: ‘‘ Endlich hat der mehr oder minder 
herabgeriickte Augenbecher, und im Falle der Vereinigung der drei- 
theilige Augencomplex, eine mesodermale Umhiillung erhalten, welche 
sich direct in das Neurilemm des zur Retina tretenden Nerven 
