36o NATURAL HISTORY OF AQUATIC INSFXTS CH. 



armed ovipositor. The work is executed by a back- 

 ward and forward sawing motion, and occupies about 

 a minute. Then the egg is pas.sed into the incision, 

 about one third of its length remaining outside ; the 

 exposed extremity corresponds to the head of the 

 future embryo. It will be seen that this is nearly 

 the same procedure as that adopted by the female 

 Dytiscus (p. 41, Fig. 3). 



The eggs of Corixa arc in general glued to sub- 

 merged objects. In certain species they are very 

 numerous and densely massed. This is particularly 

 the case with the eggs of two Mexican species (C. 

 mercenaria and C. femorata) which have long served 

 as an article of food to the Mexicans. They are 

 gathered in the lakes of Chalco and Texcuco, which 

 adjoin the city of Mexico. Reeds are set in bundles 

 in the shallows of the lakes, and upon these the 

 Water-boatmen lay their eggs, which are gathered 

 and detached by beating. They are made into cakes 

 with meal, and are said to have an agreeable acid 

 taste. Great deposits of former layings of eggs are 

 said to form at the bottom of the lakes, and to grow 

 steadily in extent.^ 



A Sialid Insect of North America (Corydalus 

 cornutus) forms large flat, rounded masses, composed 

 of two or three thousand eggs, on the leaves of trees 

 overhanging water. An extinct Corydalus of Tertiary 

 age has left countless fossil eggs in the freshwater 

 beds of the Laramie group, Colorado. The eggs arc 

 massed into elongate, cigar-shaped bundles, which 

 are 5 cm. (2 inches) long. Each is estimated to 

 ^ Girard, Traite d''Entoniologie^ Tom. III. p. 846. 



