126 



OUR HOUSEHOLD INSECTS 



laid, not singly, but in purse-like cases containing sixteen 

 each. Cockroaches are not alone in this peculiarity : a 

 somewhat similar method of oviposition is practised by 

 others of the Orthoptera, and the egg-cases of the 

 Mantidcie, or praying insects of tropical Africa, in par- 

 ticular are remarkably elegant. The egg- contain ing 

 case (Fig. 36) is a horny oblong body with rounded ends, 



FIG. 36. Egg-Case of Cockroach. A, outside view ; B, inside view, showing 

 eggs, one side having been removed. (After Miall and Denny.) 



and has a longitudinal toothed ridge along the edge, 

 which is uppermost when it is laid. This toothed edge 

 consists of the enlarged borders of a slit which, by the 

 elasticity of the material, is kept closed till pushed open 

 from within. The material of which the case is com- 

 posed is secreted by a special gland the colleterial gland 

 consisting of branching tubes, and is poured out in 

 a fluid condition into the cavity from which the case 

 will ultimately issue. It lines the walls of this space, 

 and, hardening in that position, forms a sort of hollow 

 mould of the cavity itself. Eggs are now passed into it 

 one by one, and, as it is gradually filled, its length is 

 increased by fresh additions to its inner end till it is 

 completed. 



The question may be asked, why there are always 

 sixteen eggs in each capsule. The answer is simple. 

 The two ovaries each consist of eight tubes, and no 

 more than one egg is ripe in each of these at the same 



