Dipiera: Nemocera vera, N. anomala and Eremochaeta . 431 



Hitherto I have been pointing out and defining the differences 

 between the three groups of diptera which I propose to introduce. 

 I shall attempt in the next paragraphs to take iip each group se- 

 parately and to prove the homogeneousness of the Nemocera 

 Vera and the Eremochaeta by the study of the detail of their cha- 

 racters. The JSemocera anomala^ as I have already remarked, is 

 an artiticial subdivision. 



III. Detailed characterization of the three divisions. 

 I. Nemocera vera. 



The Nemocera vera, as I said above (p. 423) „uever have a holop- 

 tic head, and hence, the differentiation of the sexes in the breadth 

 of the front and in the size and shape of the eyes, if it exists at all, 

 is reduced to a mininium". As bisection and bicoloration of the 

 eyes occur almost exclusively in connectiou with holopticism, they 

 are never met witli aniong the Nemocera vera. The relative size of 

 the head is very small. The eyes, round, oval or lugate, are placed 

 on the sides of the small head, and are separated in both sexes by 

 a more or less broad front. The very frcquently occurring lunate 

 shape of the eyes is due to the smallness of the head, in order to 

 leave room for the Insertion of the antennae. When lunate, the eyes 

 are offen approxiniate or contiguous, sometimes even confluent with- 

 out any distinct suture at their upper ends, and in some cases, at 

 their lower ends also (below the antennae). When both eyes coalesce, 

 above and below, the whole head looks almost like one eye. Such 

 a structure (some instances of which will be given presentlj') must 

 be looked upon merely as an exaggeration of the lunate eyes; it dif- 

 fers from true holopticism in that it occurs in both sexes, and often 

 Shows confluence and no suture between the eyes above the antennae. 



Lunate eyes are found in all the families of the Nemocera vera, 

 except in the Tipulidae; their frequent occurrence is characteristic of 

 some families (Cecidomyidae, Chironomidae, Cidicidae, Psycho- 

 didaej although even in these families exceptions occur. 



The Cecidomt/iae, as a rule, have lunate eyes, often confluent 

 above the front in both sexes (compare the figures of Cecid. pseudo- 

 cocciis Rübsaamen, Verh. Z. B. Ges. 1890, Tab. VI, f. 8, and C. prati- 

 cola Kieff., W. E. Z. 18;i2, Tab. I, f. 9). Such eyes, confluent or, at least, 

 without any visible suture, may be called cyclopic eyes. i) Some- 



i) A case of coalesccnce of the eyes of the common bee, above 

 the ai.tennae and without suture, has been described by Lucas (in the 

 Ann Soc. Ent. Fr. 1868, p. 737, Tab. 12, f. 1—3) under the name 

 of cyclopia; but this case is a monstrosity and not a normal occurrence. 



