REPRODUCTION IN DROSOPHILA. 



211 



the sac by means of powerful muscle fibers (m} which form a 

 cone, the axis being determined by the rod. 



The enlarged portion (c) connecting the vas deferens with 

 the ejaculatory duct borders the rod-shaped sclerite forming a 

 crescent and therefore is not pierced by it, as inspection of Fig. 2 

 might lead one to suppose. As the sclerite is a projection from 

 the plate mentioned above, the latter forms a considerable part 

 of the wall of the cavity contained in this enlarged portion, 

 which collects the sperm coming from the vas deferens. 



The mechanism that drives the sperm through the narrow 

 ejaculatory duct appears to be very simple but highly efficient. 



..IV 



m *-,~\- 



FIG. 2. Diagram of the ejaculatory sac based on the study of sections and 

 on the observation of the fresh organ. The sac has been represented as cut 

 along the sagittal plane, c, cavity connecting the vas deferens, d, with the 

 ejaculatory duct, e ; f, fluid contained within the sac; m, muscle fibers; s, 

 sclerite ; w, epithelial wall of the sac. 



Upon contraction of the muscle fibers connecting the sclerite 

 with the walls of the sac, the thick plate at the base of the rod- 

 shaped sclerite sinks into the cavity of the sac, compressing the 

 fluid therein. At the same time the portion connecting the vas 

 deferens with the ejaculatory duct is expanded, the partial 

 vacuum thus produced causing the sperm in the former to flow 

 into its cavity. The relaxation of the muscle fibers aided by the 

 elasticity of the fluid contained in the sac brings the plate of the 

 sclerite to its original position, and as a result the sperm in the 

 cavity is driven out under pressure through the ejaculatory duct. 



