PLATE 45. 45*. 
insect, as the petrifaction frequently offers itself in small 
groups of 20 or 30 specimens, lying within the compass of 
three or four inches of stone. These specimens exhibit 
more or less perfect fragments of the original, and are 
generally covered with a white, sparry matter, retaining 
minutely the structure of those particular parts from which 
it has received its form. 
The lunated tubercles on the head were apparently in- 
versed, in the recent subject, with a much thinner integu- 
ment than the other parts of the insect. In perfect specimens 
the dark colour of the limestone is always seen through the 
present sparry covering of these protuberances; while the 
rest^of the petrifaction, from the greater thickness of the 
crust, appears perfectly white and opaque. There can 
scarcely be a doubt, that the parts in question were the eyes 
in the living animal. Their form, as well as the evident 
difference of their native covering from that of the body, 
first led to this conclusion; but what places the matter 
almost beyond uncertainty, is their reticulated structure — 
This, with the help of a glass, is sufficiently visible : and 
we may observe, that such a structure, while it proves the 
nature of the parts where it is found, is also illustrative 
of the operation under which the mineral change has been 
effected — Since, only a sloiv and gradual substitution of 
fossil for organic matter could have preserved in the petri- 
faction a conformation thus mffiute. 
