This image again shows  a series of crayfish appendages embedded in a plastic block.  As mentioned on the previous page, walking legs are used for locomotion and grasping.  Depending on the  sex of the individual, the swimmerets may be variously modified.  In males, the first pair of swimmerets (called gonopods) have been modified for sperm transfer.  In females, the first pair of swimmerets (which are  rudimentary) are used for carrying the eggs and young.  The remaining swimmerets in both males and females can be used for creating currents for water circulation over the gills.  The last pairs of true appendages are called uropods that (along with the terminal telson) form the tail fan used for locomotion and egg protection.