292 



SCIENCE- GOSSIP. 



The eyes are then said to be " contiguous/' and 

 touch for a considerable distance, only diverging at 

 the top to form the " ocellar triangle." Obviously 

 this does not apply to those families — seven in 

 number — in which the ocelli, the simple eyes, are 

 absent. The familiar blowfly {Callipliora erythro- 

 cepliala) illustrates the former point. If several of 

 these are examined, some will be noticed with a 

 smaller space between the eyes than others : these 



A 





y 



Fig. 1. Siphona geniculata, dorsal vievv\ 



are the males. S'lfluna geniculata has no differ- 

 ence in the sizes of the frontalia of the sexes, and 

 the male and female may be said to be outwardly 

 identical, which is not a usual j)henomenon. 

 In the large majority of cases the sexes are 

 distinguished by what are known as secondary 

 sexual characteristics ; this includes the width 

 of the frontalia, but also comprises an endless 

 variety of brushes, of spines, of teeth, and of 

 hooks which are to be found on the limbs and 

 bodies of the males, and are absent in the 

 females. In some few cases the sexes are 



Fig. 2. Head of -S'. geniculata, lateral view. 



colom-ed in a different manner. In the hawthorn 

 fly {B'lhio horUilans) the female is an orange-red, 

 while the male is immaculate black. In a very 

 handsome fly, common in the country- — Grapltomyia 

 maoulata — the female is a light grey, barred and 

 spotted with the richest velvety black, while the 

 male, though retaining some of the black markings, 

 has on the abdomen replaced the grey by an orange- 

 red, not unlike the shade found on the female of 

 B. Iwrtnlans. As an example, the verification of 

 which is within the reach of all, I can quote the 

 lesser house-fly {Homalomyia canicularis). The 

 male has part of the abdomen a very dull yellow 



marked with dark grey bars, and the female has 

 the abdomen grey and unspotted. In these three 

 species the eyes are larger in males than in 

 females. 



It is not only on account of the sexual similarity 

 that Slplurna is noticeable. The long, geniculated 

 proboscis is interesting in many ways, and from 

 the homological point of view bears the same 

 relation to the mouth parts of Diptera as does 

 the neck of the giraffe to that of other mammalia. 

 Nothing can be more dissimilar in appearance 

 than this slender-jointed rod and the proboscis of 

 the house-fly (fig. 3) ; but let them be micro- 

 scopically examined, and the homologies of struc- 

 ture are at once apparent (see fig. 4). It is true 

 that in the process of elongation some of the 

 tracheae have disappeared. A parallel case is 

 found in the mouth of the predaceous fly, Empis 

 tesselata. The teeth, that are by no means a well- 

 known appendage to the tracheae of the nearly 

 related house-fly {M. domestical, are absent. This 

 latter loss is, however, a chai-acteristic of all pollen- 

 feeding flies, as in the hover-flies (^Syrplddae'), bixt 



•1^1 





Fig. 3. Proboscis of house-fly {Musca domestica). Showing 

 expanded labella, teeth lancet case, and palpi. 



I do not know any other genus of the Muscidae 

 in which they have disappeared. The proboscis 

 has been elongated till it is nearly as long as the 

 insect, and this extreme length, combined with its 

 tenuity, enables it to probe the long tubes of small 

 flowers similar in shape to those on the privet and 

 camomile, and to reach- their nectaries. I have 

 often watched with great pleasure this process. 

 The proboscis is inserted and withdrawn slowly 

 and with grace, the insect evidently enjoying the 

 honey sucked up by its slender tube. , 



Fig. 1 is a drawing of the fly, giving a dorsal 

 view. The individual happened to be a male ; the 

 female is, however, exactly similar. Fig. 2 is a 

 lateral view of the head of the same insect. 

 Fig. 3 is the proboscis of a house-fly {31. 

 domestica), prepared and mounted for micro- 

 scopic examination. At the base of the tracheae 

 are the teeth. A sheath which fits into a depres- 

 sion in the trunk of the proboscis is here shown 

 projecting at an angle. This contains the stylets, 

 with which many predaceous flies kill their prey. 



