a small, saclike structure in the female reproductive tract in many invertebrates, esp. insects, for receiving and storing sperm
See spermatheca in American Heritage Dictionary 4
(spûrˌmə-thēˈkə)
nounpl.-cae(-sē)
A receptacle in the reproductive tracts of certain female invertebrates, especially insects, in which spermatozoa are received and stored until needed to fertilize the ova.