528 THE SENSES AND SENSORY ORGANS. 
Weismann [2], whilst he admits that four nuclei appear in 
the cell from which the corneal lens is developed, says there is 
only one cell, and not four—one cell with four nuclei. Hickson 
says that ‘Semper’s nuclei’ have nothing whatever to do 
with the formation of the corneal facets; but these ‘are 
formed from a continuous layer of protoplasmic substance 
which underlies the whole surface of the cornea, and remains 
as a living protoplasmic lamina until the eye is fully developed, 
and then shrivels up’ [287, p. 23]. Such a statement is 
surely an anachronism ina paper published in 1885, it would 
have looked better in one written in 1850. In every case 
when such continuous nucleated layers have been described, 
subsequent observations have dispelled the illusion. 
Grenacher describes the cornea as nearly flat on its inner 
surface. I have frequently seen sections in which this is the 
case, but they are ill preserved. Specimens which have been 
kept for some time in spirit are usually in this condition. 
The convexity of the inner surface of the cornea is only 
preserved in specimens fixed in osmium peroxide. He also 
represents the remains of the membrana propria of the cone as 
the pseudo-cone [222, Fig. 63]. In other respects our de- 
scriptions and figures are very similar, indeed, almost identical. 
Grenacher’s specimens, he says, had been preserved in alcohol ; 
evidently without any special precautions, as he observes: ‘I 
came across specimens of M. vomitoria, preserved amongst 
numerous others in alcohol (W’eingeist), which had lost their 
pigment and had become white’ [222, p. go]. It was from 
these he drew his figures and description. 
The Cone.—The cone of the ommateum in the Blow-fly is 
pseudo-conic. On the seventh or eighth day of the pupa 
state, however, it consists of four transparent cells, Grenacher’s 
aconic stage. 
The pseudo-cone in the imago (Pl. XXXVI, Fig. 1, c, c) 
exhibits no trace of structure; it is surrounded by a thin mem- 
brana propria, and by several large, flat epithelial cells, loaded 
with bright crimson granular pigment. This pigment assumes 
a brown colour in chromic acid and alcohol. 
