24 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 



In the primitive blepharocericl Echuardsina, shown in Fig. 2, J, 

 the so-called "gula" or throat region, gu, extends from the occipital 

 foramen, of, to the gular or postentorial pits,, gj) (i. e., the extei-nal 

 apertnres of the invaginations forming the posterior arms of the ten- 

 torium) ; and in the syrphid shown in Fig. 1,K, secondarily formed 

 sutures demark the so-called "gular" region, gu., from the postgenae, 

 2)g. It has been shown, however, that in the Diptera the so-called 

 ••gular"' region is a '•pseudogula"' formed l)y the mesad approximation 

 and union of the postgenae (or hypostonuil areas), so that the so-called 

 ''gular'' region of the Diptera is not strictly homologous with the gula 

 of lower insects, and might be called a pseudogula to indicate this fact. 



4. The compound eyes 



The cornea of the compound eyes contains a number of facets 

 (or lenses of the ommatidia or visual elements of the eye), which vary 

 considerably in number and size. A common housefly, for example, 

 may have about four thousand facets in each eye, while there is only 

 one facet in the e3'es of some streblicls. Compound eyes with larger 

 facets are better adapted for vision at night, or in dim light, while 

 those in which the facets are smaller and more numerous are better 

 adapted for vision by day — and the image produced by the latter type 

 is probably much sharper. . 



The facets of one region of the eye may be larger than those of 

 another region, and in such cases the larger facets are usually located 

 in the dorsal portion of the eye. as in certain lilepharocerids, etc. 

 The larger facets may be in the middle of the eye, however, as in cer- 

 tain asilids, or they may be in the ventral region of the eye, as in 

 certain enipids, etc. In some blepharocerids, in which the facets of 

 the upper half of the eye are larger than those of the lower half, the 

 two regions of the eye are divided by a constriction, or narrow band 

 in which there are no facets, and a somewhat similar constriction oc- 

 curs in the postero-ventral region of the compound eyes of certain 

 bibionids. 



When the eyes are dichoptic (separated) in one sex, and holoptic 

 (contiguous) in the other, they are typically holoptic in the males 

 alone, as is true of the Leptidae, Stratiomyidae, Tabanidae, Pantoph- 

 thalmidae, Therevidae, Scenopinidae, Nemestrinidae, Bombyliiclae, 

 Syrphidae, Pipunculidae, Platj'pezidae and other higher Diptera in 

 which the eyes are contiguous, but in such empids as Flyhos, or in the 

 bombyliid Si/sfropus, and in certain C^^rtidae, the ej^es are contiguous 

 in the fenuiles also. In some Xematocera, such as the Anisopodidae 

 (excepting Mesochria), Bibionidae, Simuliidae. etc., holoptic eyes 

 ma}^ occur in the males alone, while in certain Blepharoceridae, and 

 in the Orphnephilidae. the eyes may be holoptic in both sexes. 



In some scatopsids, cecidomyids and sciarids, the narrow upper 

 portions of the compound eyes become approximated to form a narrow 

 bridge extending from one eye to the other across the area between the 

 ocelli and the bases of the antennae. This condition is called '"zygoph- 

 thalmie" by Enderlein. who considers that its occurrence indicates 

 such a close relationship in the few Nematocera in which it occurs, that 



