ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
171 
which refract the light strongly, and so resemble those which enter into 
the constitution of the tapetum of the eye of Mammals. 
The basal membrane is pierced by holes which give passage to tho 
nerve-tubes which go to the ommatidia ; these holes are arranged in 
pentagons. Seven cylinder-cones are destined for each ommatidium, 
and as they traverse the basal membrane they lose their sheath. 
The author thinks that the results at which he has arrived are of a 
kind to throw a new light on the physiology of the vision of Arthropods, 
and he directs attention especially to the fuller information which he is 
able to give of the structure of the ommatidium, as compared with that 
of his predecessors. He is of opinion that the observations of Parker, of 
himself, and even of Patten are sufficient to cause the rejection of the 
theory of retinophores ; although this was, when proposed, received with 
much enthusiasm, it was founded on errors of observation, and it is to 
be wished “ that it should cease to encumber any longer treatises and 
manuals of zoology.” 
Experiments on the eyes of Insects and Crustacea show that, in the 
Insect, a real and inversed image of external bodies is found in each 
ommatidium ; it coincides with the internal face of the crystalline cone, 
which is in immediate contact with the retinula. Although small the 
retinular image is distinct and extends over an angle of about 45°. In 
the Crustacea, in the same way, the crystalline lens forms on the retinula 
a real and reversed image of external bodies ; but, in this type, the re- 
fractive media have a very long focus and the retinula is separated from 
the lens : the interval between them is filled up by a substance which is 
the analogue of the vitreous body of vertebrates. In both cases it would 
appear that light does not act directly on the rods ; these latter can only 
receive impressions through the intermediation of the retinal cells. The 
retinal images of Arthropods are much less perfect than those of ver- 
tebrates ; but on the other hand the eyes of the former are better adapted 
for seeing bodies set in relief, and the movements of bodies. 
a. Insecta. 
Colours of Insects.* — Mr. A. B. Griffiths has determined the com- 
position of the green pigment which is found in the wings of Lepido- 
ptera and other groups ; he ascribes to it the empirical formula of C n H 10 
Ag 2 N 8 O 10 ; and, as by prolonged boiling with hydrochloric acid, the 
pigment is converted into uric acid, he suggests that it is deposited in 
the wings by wandering cells. He gives it the provisional name of 
lepidopteric acid. 
Reactions of Lepidopterous Pigments.! — Mr. F. H. Perry Coste 
has continued a line of research briefly alluded to in his former papers,! 
and has investigated the conditions under which certain yellow Lepido- 
ptera may be reddened by potassium cyanide. The following are his 
main conclusions : — 
(1) Various yellow and orange species of thePieridae rapidly become 
of a brilliant red when exposed to the action of “ sloppy-solid ” potassic 
cyanide. 
* Comptes Eendus, cxv. (1892) pp. 958 and 9. 
f Entomologist, Jan., March, and April, 1893, pp. 1-5. 
i See Entomologist, 1891, pp. 163-7 ; and this Journal, 1891, p. 458. 
N 2 
