412 W. WESCHE ON THE MALE ORGANS OF THE FLIES 



4 



special study, as they appear on a cursory examination to 

 resemble the ovipositor, and indeed may easily be taken for that 

 organ. However, they will be found to homologise, as they 

 consist of a number of plates and processes arranged round a 

 central male organ. These make a total of nine parts, and consist 

 of two lower plates {laminae basales), two upper plates {laminae 

 superioi'es), two outer hooks or claspers {forcipes inferioi'es), two 

 inner claspers {forcipes suj^erioi^es), and a central penis, which is 

 called the appendix interna, or adniiniculum. These are homo- 

 logised with the same number of parts in the ovipositor. 

 Compared with Blatta, the genitalia of Scatophaga are simple, 

 and correspond in several points with the arrangement of those 

 found in the Ifycetophilidae. 



The males in Scatojyhaga are variable in size, some being 

 smaller, and others, contrary to the general rule, larger than the 

 female. In mating the female is seized with a sudden spring 

 (when killing prey or feeding are favourite occasions), and 

 forcibly held, though sometimes fiercely struggling. We see here 

 the cause of the variability in size — superior strength is of 

 obvious advantage to the male, as well as the complicated 

 mechanism we are about to examine. Most, if not all, insects 

 which mate on the wing are provided with hooks or claspers 

 for holding the female. In Diptera this is very well marked 

 in the gnats {Culicidae) and the fantailed flies {Dolichopidae). 

 Scatophaga is well provided in this respect, as, without counting 

 the testes, or any of the internal tubes or glands, and the lever 

 figured, as No. 7, the male genital armature consists of no less 

 than ten separate pieces with distinct functions. This also 

 omits a series of setose processes which line the anterior edge of 

 the cavity of the hypopygium, but which are absent in some 

 species. 



Four paired organs are found : viz. — (1) two plates, which 

 probably correspond with the podical plates of Huxley, and 

 are so thickly haired that possibly they may be of sensory use 

 (Fig. 3). (2) Two outer hooks, with setae on the edges; I have 

 noticed these organs holding the abdomen of the female (Fig. 4). 

 (3) Two small palpi with apical bristles are within the cavity of 

 the hypopygium (Fig. 5). (4) Close to these palpi are two smaller 

 hooks (Fig. 2). Behind the hooks is the penis, which probably 

 forms a continuation of the ejaculatory apparatus, and is a 



