AND THEIR HOMOLOGY WITH THE GENITALIA IN DIPTERA. 241 



conglobate gland in contact with the containing apparatus, 

 so mixing the secretion from the gland and the spermatozoa, and 

 forming a spermatophore. This necessary movement of the 

 theca has led to its detachment from its surroundings, already- 

 discussed in section (e). (3) The containing apparatus with 

 the covering plate held down over it by the apodeme. On 

 excitement the lever would relax the muscles holding down the 

 cover, and (4) the spinus bending over would transfix a spermato- 

 phore, and transfer it to the cloaca of the female. Dr. Lowne 

 quotes Cornelius,* " who gives a description of the sexual act in 

 this insect, and describes it as being accomplished with great 

 rapidity." A fact quite consistent with the explanation of the 

 mechanism offered above. 



Explanation of Plates 19 and 20. 



The size of the drawings on Plate 20 has been regulated by 

 convenience. Their true relative magnitudes are shown on 

 Plate 19. 



The following letters are used in the plates : 



d. The extremity of the penis. 



e. Theca. 



f. Paraphalli. 



g, Hypophallus. 



h. Spinus titillatorius. 



i. Forcipes interiores. 



h. Pal pas genitalium. 



m. Great apodeme. 



o. Sacculus ejaculatorius. 



p. Ejaculatory apodeme. 



r. Convoluted plate. 



s. Cover. 



v. Articulating piece. 



Fig. 1. The genitalia removed from the cavity of the abdomen, 

 showing the natural arrangement of the parts, with the muscular- 

 structure as seen from the right. 



* Blow-fly, p. 684. 



