418 Osten Sacken: on the charaders of the thrce divisions of 



tliat a natural arn'angenient niiist be tlic result uf the study of tliose 

 Organs of the imago which are necessary for the functions of external 

 life, principally, therefore, of the organs of orientation connected with 

 the head (eyes and antennae) and in tlie second line, of the organs 

 of locomotion (legs and wings)." An arrangenient of the imagos based 

 upon sucli principles will of necessity be justified by a morc or 

 less tangible correspondence in the characters of their larvae. This 

 structural correspondence, this parallelism, of larvae and imagos, 

 among the Nemo ca^a, suffers, as far as I know, but two exceptions: 

 Mycetohia pallipes and JRhyphus; Anoplieles and Diwa. In both 

 cases almost identical larvae produce flies belonging to difterent fa- 

 milies. This unsolved problem will be discussed by me in its place. 



I shall cndeavour in the present papcr to give niy „Suggestions" 

 a further developnient. I shall try to show how a nuniber of useful 

 distinctive characters have hitherto been overlooked; how others, 

 although very well known, have not been sufficiently turned to account; 

 and how a proper application of these characters easily brought 

 about a subdivision which, I trust, will appear natural, and, I may 

 say, seif evident. 



As very superficial and erroncous notions have prevailed for a 

 long tinie about the true meaning of the subdivision of the Diptera 

 into Nemocera and Brachycera, I shall begin with an historical 

 Sketch of its origin. 



Linne, with his genus Tipida, foreshadowed more or less the 

 present division of Diptera JSemocera, but his vague definitions 

 (Syst. Nat. edit. X and XII) do not even mention the characteristic 

 length and structure of the antennae. 



In Fabricius' Systema Antliatorum 1805, under the heading: 

 Characteres generum (pag. VII) the Diptera are divided into eight 

 groups, characterized principally by the structure of the antennae. 

 The first group is defined in three words: Antennis porrectis 

 articulatis, and contains ten genera, all of which belong now to 

 the Nemocera Latr. In the other groups the genera are arranged 

 most unnaturally, and in the sequel of the book these groups are 

 not- mentioned again, and the genera are placed in a different order. 



Latreille, in his „Hist. Naturelle des Crustaces et des Insectes" 

 Vol. III [1802] i) and Vol. XIV, p. 271 [1805], became the real founder 

 of the division Nemocera. He called it: Tipulaires, and defined 



1) It is in this volume that the Diptera are for the first time divided 

 into families. 



