430 Osten Sachen: on the characters of ihe tliree dh'isions of 



I liavc already stated (on p. 427) that tlie prcscnt arrangement 

 of these foiir families must be considered as merely provisional, uiitil 

 we obtain fuitlier materials. 



The aim of this tabular arrangement is to givc a Synopsis, a 

 Condensed view, of the characters of tlie threc divisions. It is not 

 intended for a dicliotoniic table for deterniining specinicns; such 

 tables must bc arranged on a simpler plan. 



In making use of this table as well as of the other generalizations 

 whieh form the subject of this paper, it must be always borne in 

 niind that the larger the group is which we are considering, the more 

 we must look to the majority of the characters only, and the less be 

 enibarrassed by exceptions. The study of these exceptions affords a 

 peculiar interest, because in some cases they probably represent the 

 remains of a distant past, atavisms. All the Tipulidae, for instance, 

 and especially the genus Tipula. have verticillate antennae; but, as 

 an exception, the Tipulae froni New-Zealand and also from the south 

 end of South-America (especially from Chili), have no verticils (more 

 detail will be given in the sequel). Among the Nemocera vera the 

 Mycetophilidae are the only faniily which, as a rule, has no verticils 

 on the antennae; but an exceptional Platyura from New-Zealand has 

 them Short, but quite distinct. The same Platyura has the eyes 

 contiguous on the front, which is again an exception among the 

 Mycetophilidae. We thus seem to witness the evolution of generic 

 characters. It is well-known that New-Zealand and Chili abound in 

 archaic forms of Diptera, and it is very much to be regretted that 

 the materials which we have from those countries are so scanty. 



The three large divisions of the Diptera which we are considering 

 belong to those that are not provided with the protective System of 

 macrochaetae described in my paper on that subject (Trans. Ent. 

 Soc. London 1884). In some rare cases, among the genera of these 

 divisions, stouter hairs occur, principally on the thorax, but their 

 occurrence is merely sporadic; they do not represent a whole system, 

 like the macrochaetae among the Cyclorrhapha, or in the families 

 Asilidae, Dolichopodidae etc. They may have the same protective 

 or sensitive fnnctions: but they are conspicuous in one genus and 

 wanting in the next; they cannot therefore, without further proof, be 

 considered as homologous with the regulär macrochaetae. The genus 

 Pachyneura shows hairs of that kind, but they do not exist in its 

 next relative, the genus Bilno. Some Sciophilae likewise possess 

 such pseudo-macrochaetae. I leave the matter to the investigation by 

 trained physiologists. 



