224 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



relation to the spermathec^. Dr. Michaelsen noias tnat 

 the reduction of the posterior prostates and the forward 

 movement of the sperm-ducts has been necessarily accom- 

 panied by a reduction of the anterior pair of spermathecse. 

 So far as we know, this has been the case in four only of 

 the Dichogaster species, Dichogaster Damonis, for instance, 

 being an exception. 



On examination, D. Townsendi is found to greatly resem- 

 ble D. Damonis in almost every particular, except that the 

 former possesses two pairs of spermathecae. It is impossi- 

 ble to separate these two species and refer them to different 

 genera. Among the other species, Microdrilus saliens dif- 

 fers from D. Braunsi principally in the possession of two 

 pair of spermathecae, but in other respects the reduction of 

 the prostates and the forward movement of the sperm-ducts 

 have been completed. In another species, D. Ribaucourti, 

 the forward movement of the sperm-ducts has alone been 

 accomplished, the two pairs of prostates and the two pairs 

 of spermathecse remaining. 



As the genus Dichogaster is now presented, it is impossi- 

 ble to segregate any one of the species without destroying 

 the whole genus. If, for instance, we begin by assigning 

 D. Ribaucourti to the genus Benhaniia, on account of its 

 two pairs of prostates and its two pairs of spermathecse, 

 then we must, to be consistent, refer D. Tozunsendi also to 

 this genus; but if D. Townsendi is placed in the genus 

 Benhaniia, D. Damonis must likewise be placed there, as 

 these two species differ only in the presence or absence of 

 the anterior pair of spermathecse. Similarly, if we transfer 

 D. saliens and D. Crawi to the genus Microdrilus, then, 

 also, must be referred to this genus several other species 

 which do not possess posterior prostates. 



As will be seen from the above, it is impossible to segre- 

 gate any of the species and place them in other genera 

 without destroying the whole genus. At the same time, we 

 see that the most constant character is the position of the 

 sperm-ducts in the center of somite XVII; but even this 

 constancy of character is shaken by the position of the 



