IN THE GENUS ANTHOPHORABIA. 163 
distinguishing forms depend, exists in the most perfect of the eyes of the male, those of 
the vertex, I am not yet entirely satisfied. I have certainly detected appearances, in the 
nymph or pupa state of the male (fig. 10 2), which have led me to think that the Jens is then 
present; but I have not satisfied myself of this in the perfect insect, and hence the ap- 
pearances seen may have been due simply to the vitreous body, as it exists in some of the 
lower forms of the eye among the Annelida. 
‘Whether, however, the lens does or does not exist, is of little importance with reference 
to the simple question as to whether these structures in the male Anthophorabia are the 
true homologues of the eyes in the female. That they are so I have not the slightest 
hesitation, after what I have shown, in affirming. The presence of a cornea, which covers 
a chamber lined with pigment, is sufficient proof to the physiologist and anatomist of the 
nature of the function of the structure. 
The form of the cornea, however, shows that the field of vision is very limited. The 
cornea, as already stated, is but very slightly convex, being almost level with the surface 
of the head. This fact may have conducted some to the opinion that these are not visual 
organs. But neither the actual size of a simple eye, its form, nor the degree of its con- 
vewity, has any necessary connexion with the simple faculty of perceiving light. The 
convexity of the cornea has relation only to the extent of angle, or field of sight. The 
more convex, and the more elevated the eye is above the surface of the head, the greater 
proportion of a sphere does it necessarily include; and, as long ago shown by Prof. Müller, 
the greater the segment of a sphere formed by the eye, the greater is its expanse, or field 
of vision; while, on the contrary, the flatter or more depressed it is the more limited is 
this field, and the shallower the chamber the shorter is its focal distance. 
The presence of the Jens in the simple eye is essential to rendering the sight of images, 
and the appreciation of form, more or less perfect; and it does this in proportion to the 
more or less correct relation which it bears to other conditions coexistent with it. 
With regard to the nerves supplied to these eyes, I may state that although I have not 
been able to trace those of the vertex so satisfactorily in the male Anthophorabia as I 
could have wished, owing to the numerous muscular fibres which run parallel to them, 
yet I have succeeded in tracing the optic nerve (d d) from the side of the cephalic ganglion, 
or rudimentary brain (d), transversely, in the direction of one of the lateral ocelli (2) ; 
and I believe, also, that I have distinguished the nerve which goes to the middle eye of the 
vertex (c). The nervous trunk which is given to the middle ocellus in Insects I have 
already shown, in my paper on P/eronarcys*, is formed of two closely approximated 
nerves, one from each cephalic ganglion, as found by a careful dissection of that insect, and 
also of several Hymenoptera; and this probably is its condition in all other insects with 
three ocelli on the upper surface of the head. 
I may here also refer to what is stated in my paper on Meloet, that there seems reason 
to think that in the Arachnida, and probably also in insects, the ocelli originate in the 
same way as the dermal tubercles, from which they appear to differ chiefly in the mod 
of development of their nuclei and nucleoli. 
* Linn. Trans. vol. xx. p. 440. + Ibid. vol. xx. p. 342. 
