626 THE MICROSCOPE. 



portion of them, that fitted for seeing in the air, is fixed 

 on the upper part of the head, the lower portion, for 

 seeing under the water, is placed at the lowest part, a 

 thin division separating the two. 



Sir John Lubhock, writing of aquatic insects, says : * 

 "Though most of the great orders are represented, no 

 aquatic Hymenoptera or Orthoptera had till now (1864) 

 been discovered. Great, therefore, was my astonishment, 

 when I saw a small Hymen opterous insect, evidently quite 

 at its ease, and actually swimming by means of its wings, 

 At first I could hardly believe my sight ; but having found 

 several specimens, and shown them to some of my friends, 

 there can be no doubt about the fact. Moreover, the same 

 insect was again observed, within a 'week, by another ento- 

 mologist, Mr. Duchess, of Stepney. It is a curious coinci- 

 dence that, after remaining so long unnoticed, this little 

 insect should thus be found almost simultaneously by two 

 independent observers. Mr. "Walker at first considered 

 the insect to be Polynema fuscipes, but though allied to 

 that species, it is not identical with it. So completely 

 aquatic is it in its habits that it can remain immersed for 

 at least twelve hours ; but it nevertheless requires to come 

 to the surface at certain intervals to renew the air in its 

 tracheae. It is uncertain whether P. natans can also use 

 its wings in flight. They are at any rate not easily incited 

 to do so. It is a very minute species, and well fitted for 

 microscopical observation, the female measuring 0'3S of an 

 inch, and the male 0'42." 



Dytiscus marginalis, derived from dutes, a diver. Larva 

 narrow, body composed of twelve segments, including 

 head, which is large and strong, bearing antenna, and 

 armed with two powerful jaws. Several varieties of this 

 beetle are met with in fresh and still waters. The Iarva3 

 feed upon other aquatic larvse, such as the Gnat, Dragon- 

 fly, &c. The suckers on the legs, the feet, &c. are very 

 interesting objects, and should be mounted for viewing 

 both as transparent and opaque objects. 



To the Orthoptera belong Locustina, Gryllina, and Ache- 

 iina, all herbivorous insects. The first is represented by our 

 well-known Grasshopper (Gryllus viridissimus), the secor d, 



(1) Joury,. Micros. Soc. vol. iv. p 139. 1864. 



