SCIENTIFIC SUMMARY. 
375 
Specific gravity . 
Solid constituents (total) per cent . 
Ferric compounds, per cent . 
Injurious organic matter 
A. B. 
1-024 1-022 
4-0780 4-1005 
0-1106 0-0724 
ratio = 3 ratio =2 
The water A contained a large quantity of Algae and Infusoria. {Ann. 
Mag. Nat. Hist., September, 1881.) 
The Egg-cases and Young of the Mantidce . — M. C. Brongniart brought 
with him from Algeria some of the curious egg-cases formed by the 
species of the genus Mantis, and has communicated to the French Aca- 
demy the results of his observations on their structure and on the hatch- 
ing of the eggs ( Comptes Rendus, July 11th, 1881). He says that the 
structure of these egg-cases ( oothecce ) differs but little in the different 
species ; they are attached to the branches of shrubs and to stones, and are 
generally pear-shaped, with the smaller extremity upwards. Externally 
they appear to be strongly furrowed transversely, and if cut through in the 
direction of these furrows, show a circular central chamber containing the 
eggs, surrounded by a sort of frothy envelope. Each egg-case consists of 
about twenty storeys of chambers, and each of the external furrows repre- 
sents a storey ; each storey of the central chamber is divided into two cells 
by a thin antero-posterior partition, and communicates in front with the 
outside -world by a sort of flattened neck, the edges of which, in the form of 
scales, are bent and laid one over the other. Each of the central cells 
contains about a dozen eggs, so that there are about twenty-four on each 
storey ; and the eggs are arranged symmetrically, so that the portion of the 
egg which will constitute the apex of the abdomen is towards the outer 
wall of the case, while the part representing the head is turned obliquely 
forwards, and the whole of them are brought close together. Owing to 
this arrangement, the larvae, when hatched, merely have to push straight 
forward in order to escape from the case. Each egg is contained in a sort 
of gummy cell. 
In the construction of the egg-case the insect employs its abdomen and 
elytra. The female Mantis clings to a branch, and then exudes a sort of 
frothy, somewhat transparent liquid, which it holds up by means of the 
extremity of its elytra. Of this it constructs the first storey of its egg-case 
in the form of a spherical hood, the business being effected by the abdomen, 
which kneads the frothy substance and spreads it in successive layers with 
the assistance of the cerci. The eggs are expelled from the abdomen 
together with a small quantity of the frothy liquid, which serves to form 
the cells in which they lie. 
Soon after impregnation, which generally takes place in September, the 
female builds her egg-case and deposits her eggs, which hatch out in May 
and June, and each young larva, while still quite soft, advances towards 
the aperture of its cell in order to issue from it. M. H. de Saussure gives 
the following account of the emergence of the larva. He says : — ‘ The little 
larva has now to escape from the cell in which it is enclosed, and, as it is 
too weak to make use of its feet, nature comes to its assistance by means of 
a peculiar contrivance. The surface of its body is clothed with a chitinous 
substance, upon -which are developed some spines directed backward. By 
