ON THE BRITISH SPECIES OF SIMULIUM. 25 



much less developed than those of the female, the mandibles being absent in the 

 former sex. This is not the case ; the male Simulium of several species examined 

 microscopically by the writer had both mandibles and maxillae fully developed, 

 and these organs only differed from those of the female in being somewhat more 

 pointed and in having only fine hairs instead of sharp teeth along their margins ; 

 besides this, the labium has more numerous sensory papillae in the male than in 

 the female. Lt.-Col. Alcock, in his recent book. Entomology for Medical Officers, 

 states that the mandibles of the female are toothed on the inner edge, the maxillae 

 on the outer. This is indeed the appearance under a low magnification, but if a 

 sufficiently high power be used, it can be seen that both mandibles and maxillae 

 are toothed along both edges. No specific differences were observable in the 

 mouth-parts. 



Alcock has called attention to the well-marked sensory vesicle in the second joint 

 of the palpi. So far as I am aware this is the only reference to this organ in the 

 literature of the Diptera, but I believe its study in this and related families of flies 

 might yield valuable results from the point of view of phylogeny. I have noticed 

 a very similar structure in Mycetophilidae, and (in a reduced form) in certain 



BlEPH AROCERIDAE . 



Abdominal scale. — The peculiar structure characteristic of this family, situated 

 at the base of the abdomen and clothed w^ith long hair, has sometimes been regarded 

 as belonging to the abdomen and sometimes to the thorax. After having made 

 careful dissections of cleared specimens, I am convinced that it represents the first 

 abdominal tergite. It is more or less completely divided into a large dorsal and two 

 smaller lateral pieces, and seems to be in some way connected with a very large 

 internal development of the hind coxae. 



Male genitalia. — -These have been described by Lundstrom, but it is perhaps advis- 

 able to give a short redescription to explain the terms used. As in other Diptera, 

 the genitalia are extremely important for specific distinctions. The ninth tergite 

 (lamella terminalis) is well developed and entirely covers the other organs, which 

 in the dry specimen can therefore only be seen from the ventral side. It has attached 

 to its posterior margin three small chitinous pieces, of which the two lateral ones 

 {appendices superae or oheren Anhdnge) are more or less hairy. These appendages 

 undoubtedly exhibit useful specific characters, but I have not paid much attention 

 to them, as, in order to facilitate the examination and drawing of the more important 

 ventral parts, I have usually dissected aw^ay the ninth tergite with the appendices 

 superae attached. The most important parts are the large side-pieces (appendices 

 intermediae or Zange) together with the claspers which are articulated to them. 

 Owing to the absence of the ninth sternite, these organs have taken up a more ventral 

 position than usual in the Nematocera ; their structure can usually be made out 

 without dissection even in a dry specimen. Between the ninth tergite and the 

 side-pieces, and more or less completely hidden by them, is the adminiculum, with 

 its appendages (Arme and Griff el). This organ, though subject apparently to some 

 amount of individual variation, provides one of the means of separating certain 

 closely allied species. 



Tarsi. — Important specific characters are to be found in the thickness and relative 

 lengths of the joints of the front tarsi in both sexes, and of the hind tarsi of the 



