THE OOTHECA OF AN ASILID. 611 



abdomen-tip round and rovind the circumference of the ootheca 

 now and then stopping this movement to prod over the surface 

 except around the edge — when it was probably ovipositing, but the 

 abdomen-tip, as in the case of a Mantis forming its ootheca, waa 

 concealed by the colleterial matter. In plan the ootheca is rough- 

 \j a pointed oval, in transverse section roughly circular, and the 

 pointed end is the part of the ootheca first formed ; the large end, 

 which is more or less flat, is finished oiF by the insect working the 

 abdomen-tip around the ootheca from the circumference gradually 

 to the centre, where the colleterial matter is broken ofi", leaving 

 a small knob or protuberance. About an hour after its construc- 

 tion, the egg-case is firm on the exterior and, although more or 

 less moulded and wrinkled where the eggs happen to be near the 

 surface, is smooth and of a waxy- white with a slight gloss. The 

 egg-case occupied the insect about an hour in the making, and 

 it then flew away. The ootheca of this species varies much in 

 size according to the number of eggs contained : this particular 

 example was three-eighths of an inch long and three-sixteenths 

 broad and deep at its greatest girth and depth. The eggs are 

 iisually laid in two tiers, but with fewer in the upper tier (lower 

 tier in the natural position of the ootheca), as shown in Plate A, 

 Figs. 1, 2 and 3. They are slightly cemented together and to the 

 twig by the natural secretion of the ovaries. Outside the eggs, 

 and covering them entirely, is the thick wall of colleterial 

 matter (Fig. 2, CM.) ; the eggs are excluded whilst a supply of 

 colleterial matter is kept up over the exterior eggs, so that they 

 are not visible whilst being deposited. They are laid in rather an 

 irregular manner, as may be seen in Fig. 3, where the outer cover- 

 ing has been partly dissolved away with benzine, exposing the 

 eggs. The outer covering is not hard and horny chitinous matter 

 like the egg-cases of some species of Mantis, but is moderately firm 

 and microscopically porous, owing to included air-bubbles, some- 

 what like the spongy outer wall of some of the less specialised 

 Mantis oothecae. These Asilid egg-cases, however, often resist the 

 weather for several months after the larvae have hatched out. 



The colleterial glands of the $ are two long colourless tubes, 



