28 



accordingly splits on either side along this line. Once started, the 

 slit extends from nearly the top of the shell to within a third of the 

 bottom, probably by the protrusion of the soft body of the larva. 

 An egg may occasionally be found with the larva forming a small 

 protrusion on either side in this way. If the effect is aided by any 

 cutting action of the points, due to movements of the larva, it must 

 be within very narrow limits, as the extremities of the larva maintain 

 their position unmoved till after the slitting takes place. The larva, 

 on the relief of the tension, is free to move, and extricates itself from 

 the shell by one of the two slits. 



When hatched the inflation does not at once disappear, but 

 remains and even extends to give increased bulk to the young larva ; 

 this happens equally with the larv.'e of other viviparous species of the 

 same genus, where inflation is not wanted to rupture an egg-shell. 

 Its probable use is to give a more solid base for muscular action 

 than is to be had from the flaccid skin of the empty young larva. 



At the further moults of Orina larva, inflation is again brought 

 into use, its object being to rupture the effete larva skin. In each 

 instance the larva is very fat and the skin fairly tense when the stage 

 is complete and moulting imminent, and a slight further tension by 

 inflation suffices to rupture the old skin. There are now no hatch- 

 ing spines, the site of the rupture (the thoracic dorsum) being deter- 

 mined by sutures provided in the old skin. The newly moulted 

 larva may be seen to contain several large air-vessels, and that these 

 are in the alimentary canal seems clear by their escaping by the 

 mouth when considerable pressure is applied to the larva. The 

 process of moulting is here very different from that obtaining in 

 Lepidopterous larvae ; in these the new larva creeps out of the old 

 skin, the tension necessary for rupture being obtained by the new 

 larva, so to speak, creeping forwards into the front segments of the 

 ■old skin, and the empty skin is left more or less contracted and 

 folded together, especially behind, where it was pushed backwards. 

 Our beetle, on the other hand, leaves his skin fairly representing the 

 larva, especially when it is not distorted by the opening allowing it 

 to fall together again irregularly. 



The process is, in fact, very much the same as that by which most 

 Lepidoptera leave their pupae ; it probably obtains, with variations 

 and specialisations, in all those instances amongst insects in which 

 the skin to be cast has more or less solidity. 



The male of the higher Psychids also resorts to inflation when 

 introducing the abdominal segments into the larval sac and pupa 

 case of the female, in order to secure the necessary solidity by 

 which muscular action can be effective. 



We find, then, that insects secrete gas into their alimentary canals 

 in order, at various critical points in their economy, to increase their 

 bulk. The object of this increase of bulk is, in a large number of 

 instances, to produce tension within, and so rupture, an egg-shell, a 

 larval or pupal skin, or a cocoon. This is so common and universal 



