OR TWO-WINGED FLIES. 345 



It is a remarkable circumstance, that although the 

 majority of the insects of this Order lay eggs, a few 

 produce living larvae, and may thus be called vivi- 

 parous, whilst a rather larger number actually retain 

 their progeny in the interior of their bodies until they 

 have attained the pupa state. The latter singular 

 mode of reproduction, coupled with some peculiarities 

 in the organization of the perfect insects, long since 

 gave rise to the separation of the creatures mani- 

 festing it from the rest of the Diptera as a Suborder, 

 and some authors, with Dr. Leach at their head, even 

 raised this group to the rank of a distinct Order. 

 For this, however, there appears to be no sufficient 

 reason, and I shall therefore regard the pupa-bearing 

 Diptera (Pupipara) as a Suborder; whilst the re- 

 mainder of the Order, consisting with but few excep- 

 tions of oviparous species, is divisible, by means of 

 characters furnished by the antennae and palpi, into 

 two other groups, so that we get three primary 

 groups (or Suborders) of two-winged Flies. 



Suborder NEMOCERA. 



In the first of these groups the antennae are usually 

 longer than the head, and composed of at least six 

 joints, but generally of ten or more, forming filiform 

 or necklace-like organs, whence the name applied to 

 the group. The antennae are frequently long, and 

 furnished with tufts of fine hairs on the joints, or 

 sometimes completely plumose, but never, as is often 

 the case in the second Suborder, terminated by a 

 single long bristle. In other cases they are scarcely 

 longer than the head, but even when shortest, the 

 terminal joints are never suddenly reduced in size. 

 These insects are further distinguished by the great 



