THE COMPOUND EVE OF THE BLOW-FLY. 527 
appear to consist of a thin capsule, from which a fluid of high 
refractive power may be seen escaping. 
From the above facts I arrive at the following conclusions: 
(1) The cornea consists of a cuticular membrane with lenses 
beneath it. (2) That the lenses are each developed from four 
cells. (3) That the lenses consist of a stroma infiltrated with 
an oil-like fluid. Hickson [287], without troubling himself 
about my facts, takes exception to this view, and says he sees 
nothing to justify it. 
The Nuclei of Semper.—The ‘ Nuclei of Semper’ play a very 
important part in many of the descriptions of the compound 
eye hitherto published, although it is difficult in all cases to 
know what nuclei are referred to. 
Claparéde, in 1860, wrote: {203] ‘In the spring of last year 
I travelled from Altona to Paris with Carl Semper, who was 
about to depart for the Philippine islands’; and we learn that 
Semper gave him a box of slides of insects’ eyes, and pointed 
out to him ‘four nuclei between the cornea and crystalline 
cones,’ which Claparéde determined to name ‘Semper’s 
nuclei.’ 
Now, fortunately, Claparéde figured these so-called nuclei 
(203, Fig. r], and it is evident from his figure that he had not 
nuclei before him, but a lens split into four parts. 
Claparede also figured the partially-developed eye of Sphinx 
Euphorbiz, and represented the nuclei of the cells from which 
the corneal lens is developed, he also called these ‘Semper’s 
nuclei’ and these nuclei have been confounded with the four 
segments of a split lens ever since. 
Nor is this all. As Claparéde has shown, and as is perfectly 
clear in my preparations, numerous nuclei are seen in relation 
to the cone, cornea and surrounding cells at one period or other 
of development, and it is exceedingly difficult to identify 
‘“Semper’s nuclei,’ so that various nuclei have been described 
as ‘Semper’s’; this has led to considerable confusion. I shall 
therefore cease to speak of ‘Semper’s nuclei,’ and designate 
the nuclei as corneal or nuclei of the cone, or of the pigment 
cells. 
35 
