136 
THE GEOLOGIST. 
These ova are deposited, according to M. 
Guerin-Meneville, by Hemipterous (Xoto- 
nectid) insects; the most abundant being the 
Corixa femorata ; the other (which lays the 
larger eggs) being the Notonecta unifasciata. 
They are said to fly about the water in my- 
riad's, and occasionally plunge below the sur- 
face to the depth of several feet, there de- 
positing the eggs. The Indians collect the 
eggs, by placing bundles of reeds in the 
water, which in twelve or fifteen days get 
covered with millions of ova ; these they dry 
for an hour or two, and remove from the 
rushes, and sell as an article of food.* 
M. Yirlet d'Aoust remarks that probably 
an analogous origin of oolite has existed in 
all geological epochs ; and he points out 
some of tlie conditions of certain oolites 
tliat favour this view, — indeed, he seems to 
think that nearly, if not quite, all oolites, 
calcareous and ferruginous, have been formed 
in this way.f 
The oolitic travertine of Tezcuco is also 
described by Mr. E. B. Tylor, in the inte- 
resting narrative of his travels in Mexico, 
entitled ' Anahuac ; or, Mexico and the 
Mexicans, Ancient and Modern,' 1859, al- 
ready reviewed in the ' Geologist.' At page 
156, he says : — 
" When I look through my notes about 
Tezcuco, I do not find much more to men- 
tion, except that a favourite dish here con- 
sists of flies' eggs fried. These eggs are de- 
posited at the edge of the lake, and the In- 
dians fish them out and sell them in the 
market-place. So large is the quantity of 
these eggs, that at a spot where a little 
stream deposits carbonate of lime, a pecu- 
liar kind of travertine is forminof, which ^. e 
. , p • 1 11 1 ' ji lis;. 9. — Piece of white Hastiiio;s 
consists of masses of them nnbedded m the Sand, from the East Cliff, Has- 
calcareous deposit. The flies which pro- tings, showing long linear ver- 
duce these eggs are called by the Mexicans tical holes {b, c), in section; a 
' axayacatl,' or ' water-face.' There was a surface. (Xat. size.) 
celebrated Aztec king who was called Axayacatl ; and his name is in- 
dicated in the picture-writings by a drawing of a man's face covered 
* M. Virlet d'Aoust gives much interesting information ahout this substance (termed 
Haoutl), in the culinary and antiquarian points of view. See also a notice by M. Gueriu- 
INleneville, translated in the ' Annals of Nat. Hist.,' ser. 3, vol. ii. p. 313. 
t See also, ' Geologist,' Vol. IT. p. 73. 
