What is the function & location of testis sac & seminal vesicles in earthworm.

Pheritima posthuma [Earthworm] is a bisexual organism i.e;Both the sex organs are present in the same individual.It contains two pairs of testes present in segments 10 and 11 [1 pair in each segment] and they are surrounded by a bag like structure called testes sac.Each testes has a Vasadaferentia that run parallel to each other till segment 18. However, the sperms produced by testes are nourished by the  Seminal vesicles. Here you need to remember one thing that Spermatheca present in Earthworm stores the sperms received from the other individual and helps as a storing part of sperms.These Seminal vesicles are present in segment 12.