286 OUR HOUSEHOLD TNSECTS 



abbreviated, the former are entirely absent. When 

 present, they consist of an extremely delicate mem- 

 branous expansion supported on a few nervures; they 

 may be seen in one of their most beautiful forms in such 

 an insect as the Water Boatman (Notonecta glaucd). 

 The bed-bug (Plate VI.) has no hind- wings at all. 



But there is a further puzzling peculiarity connected 

 with the wings of the Hemiptera that is worthy of 

 thoughtful consideration. Those species in which the 

 wings are usually more or less imperfectly developed 

 occasionally yield individual specimens in which the full 

 degree of development is attained, all the parts being 

 present in their proper proportions. Such cases are 

 usually rare, sometimes extremely so, and the causes 

 which produce the fully matured forms still await dis- 

 covery. Take, for example, a very common insect, the 

 so-called Ditch Skater or Water Cricket ( Velio, currens). 

 Every one will remember to have seen this creature 

 living gregariously on the surface of ponds or streams, 

 skating about in lively fashion, like a company of spiders 

 enjoying an aquatic picnic. Almost always this insect 

 is entirely destitute of wings, showing not even the 

 merest rudiments of them. And yet, very occasionally, 

 amongst a crowd of specimens, all of the ordinary form, 

 there may be detected an individual with fully formed 

 elytra and wings, and therefore capable of flight. But 

 the occurrence is a most exceptional one, and the dis- 

 covery of a fully developed Velia always marks a red- 

 letter day in the diary of an hemipterist. And the 

 same thing holds good of the majority of those bugs 

 which as a rule have undeveloped wings. 



Now, as our domestic pest is one amongst the number 

 of these unfinished forms, the question arises whether it 

 ever assumes the fully winged condition, and if so, what 



