MUSEUM OF COMPARATIVE ZOOLOGY. 53 
sense, at least, that I understand the tenor of his criticism (p. 415) of 
Grenacher’s belief: “‘ At present the origin of the retina of the simple eye 
cannot be said to have been determined ; I have sought in vain for any 
reliable indications as to its origin. Dr. Grenacher believes it to arise 
by a modification of the cells of the hypoderm. His arguments in favor 
of this origin are very unsatisfactory, and apparently indicate that the 
vitreous, and not the retinal elements, arise from this layer.” 
The conclusions reached by Schimkewitsch (84) place him also with 
those who regard the retina as an outgrowth of the cephalic ganglia. He 
says (p. 10) : ‘‘ According to my observations, the eye of Epeira and of 
other spiders may be divided into two quite distinct parts: one part we 
call epithelial, the other part retinal or neural. The first embraces a lens 
and a vitreous body, and is separated from the second by a pre-retinal 
membrane. The retinal part is formed by a collection of terminations of 
the fibres of the optic nerve; each termination is formed by an enlarge- 
ment of the fibre, which supports, in the case of Epeira, a double bacillus 
and nuclei. The two parts [epithelial and retinal] are enveloped by a 
membrane —a prolongation of the neurilemma of the optic nerve — which 
merges into (se confond) the subcutaneous connective layer and the pre- 
retinal membrane (/ame).” At p. 14 of the same paper he adds: “ The 
existence of a pre-retinal membrane is an argument —and such is also 
the opinion of Graber — in favor of the development of the retina at the 
expense of a neural rudiment, and not at the expense of an epithelial 
reduplicature, as Grenacher supposes.* Besides that, we have the very 
important observations of Bobretzky, who shows that the retina of the 
compound eyes of the crayfish is certainly developed at the expense of the 
neural rudiment.” His general conclusion on this matter is summarized 
in the following words: “Les couches épitheliales et mésodermiques 
prennent aussi part 4 la formation des yeux, comme cela a lieu chez les 
Vertébrés.” 
In his more recent paper on the embryology of spiders, Schimkewitsch 
(°84*) does not deal with the origin of the eyes. 
The answers to the questions concerning the source of the retina and 
the method of its formation, now furnished by Locy, seem adequate to 
* A part of the argument implied in the above quotations from Schimkewitsch 
does not appear directly from the quotations themselves, but rests upon his interpre- 
tation of ‘‘the membrane which merges with the pre-retinal membrane and with the 
so-called subcutaneous layer.” These three structures are, in his opinion, connective 
tissue, and therefore of mesodermice origin. 
Further along in the present paper this view will be discussed, and an explana- 
tion will be offered of what seems to be the cause of the author’s apparent error. 
