THE society's NOTE-BOOKS. 189 



legs. It is possible that they may have lived on the gnat larva, or 

 have become attached to the insect at the time of its last meta- 

 morphosis. 



These mites are the larva of Aiax histrionicus or Hydrachna 

 histrionica of Hermann. They are very common in tanks and 

 stagnant water, and attach themselves to almost anything that has 

 been or is alive in the water. 



C. H. Griffith. 



Larva of Ant-lion. — This larva has no mouth, but instead two 

 horny fangs resembling jaws, which are toothed upon the inner 

 margin, and terminate in sharp points. These jaw-like appendages 

 are hollow, and serve not only for seizing but for sucking the 

 juices of the insects, for which the animal so cleverly contrives a 

 pitfall. The mandibles in front of the head are curiously made, 

 being deeply grooved throughout their entire length, and permit the 

 maxillae, or inner pair of jaws, to play up and down them. 



E. E. Jarrett. 



Macrotoma Plumbea. — Mr. E. Smith has found this insect, 

 which is very much like the Fodura, only about three times as 

 large, in two different places : — ist, he finds it plentifully in his 

 cellar — those found there are lead-coloured ; 2nd, on a wall at the 

 bottom of his garden — these assume a black tint. Is the 

 difference in colour due to the light in which they live, the struc- 

 ture of the scales and the insects themselves in all other respects 

 being identical ? 



E. Smith. 



Colours of Beetles' Wing-Cases. — This question is a much 

 wider one than is supposed by many. Diffraction is in many 

 cases an important factor, in others it is subordinate to thin plate 

 iiitej'ference^ and both are frequently controlled^ or at all events 

 modified, by the presence of various colouring matters. Thus it 

 happens that the phenomenon is a somewhat complicated one, 

 and any one elytron must be taken on its own merits and subjected 

 to careful optical and chemical examination before a full exj^lana- 

 tion of its chromatic phenomena should be ventured upon. There 

 is work here for the student of insects where he has an almost 

 un worked field, and the certainty of doing new work. I have 

 myself made a partial examination of the wing-cases of Cantha- 



