120 Objects for the Microscope. 



association of place and time will enhance the pleasure 

 ten-fold. 



There is not any small work that I know of on the 

 classification of the Diptera : the best manual of British 

 Flies is that of the ' Insecta Britannica/ in three volumes- 

 too expensive and too scientific for popular use.* There- 

 fore these slides of whole-mounted Diptera, with the brief 

 descriptions of this catalogue, will be the more valuable, as 

 giving the young student his first introduction to a family 

 he will become better acquainted with hereafter. 



Very briefly let me preface the examination of the first 

 slide with a list of the principal families into which natu- 

 ralists have divided the Diptera. As the Coleoptera are 

 known by the joints of their tarsi and structure of their 

 antennae, so the Diptera are classed according to the form 

 of the antenna? and the veining of the wings. 



There are two great groups, Nemocera and BracJu/ura. 

 The Nemocera comprises all the TipulaB, Gnats, Midges, 

 &c., which have long antenna?, from six to ten-jointed, and 

 inserted in front of the head between two large compound 

 facetted eyes. The slides of head of Tipula and head of 

 Gnat will illustrate this better than any description, and 

 enable us at once to recognise one of the Nemocera. A 

 slide of a whole Gnat and of a Ptychoptera will give 

 a better lesson on their general structure, if carefully 

 examined, than any book. 



CULEX PIPIENS. 



The common Gnat, both male and female, should be 

 mounted, as the former only has the beautiful plumed 

 antennae, and the latter only the apparatus called the sting, 

 of the Gnat, and described under " Head of Gnat/' Its 

 wing is often mounted as a separate object, to show the 

 scales, and has therefore been noticed with the wings of 

 other insects (page 89). But as this little fly is one of our 

 most common acquaintance, though not a very pleasant 

 one, a slight sketch of its habits will be interesting. 



* Insecta Britannica : Diptera, by Walker. Histoire Naturelle des 

 Insectes : Dipteres, by Macquart. 



