MALE ORGANS OF REPRODUCTION 133 



with the system there are usually certain glands of a mucous nature and 

 of considerable size ; those of the female are designed to provide the 

 ova with a superficial covering, by which they are in many cases 

 attached either to one another or to some stationary object. The 

 external opening of the male tract is at the end of a chitinous penis ; 

 that of the female is a dilatable chamber with a muscular wall. The 

 fused portion of the female tract may become very highly developed in 

 the pupiparous forms, in which it contains the larva during the period of 

 its growth and development. 



Much yet remains to be investigated regarding the relations of the 

 sexes in the Diptera. It has been said that the spermathecae, or the 



dilatations on the efferent duct of the tract in the female, 



. i i r i i ^i Relations of sexes 



contain the spermatozoa derived from the male. The 



female, once having received a supply, can go on developing her ova in 

 several batches, without being dependent, so far as is known, on a second 

 copulation. But it is not known with certainty at what period of the 

 growth of the ova fertilization takes place, or how soon after emergence 

 from the pupal state the two sexes meet. There appears to be some relation 

 between the time at which the first feed is taken and the time at which 

 copulation occurs, which may perhaps account for the extraordinary diffi- 

 culty which is sometimes met with in persuading newly-hatched flies to 

 feed. There also remains to be explained the well-known difference 

 which is found in the proportions of the two sexes. When breeding 

 mosquitoes, for instance, a large majority of those which emerge are 

 males, while on the contrary there are some species of Tabanus and 

 Haematopota of which the female is a common fly, and the male ex- 

 tremely rare. The difference in numbers in the latter case is far too great 

 to be accounted for by the more obtrusive habits of the female. The 

 conditions suggest that the male, once having copulated and fulfilled 

 its purpose in the propagation of the race, dies off, leaving the female to 

 live as long as she has eggs to lay. The point may possibly have a 

 practical interest in cases in which both sexes are blood-suckers. 



The male organs are confined to the posterior portion of the abdomen, 



and are only of interest here in that the observer 



, . . , The Male Organs 



should be able to recognize them when met with 



during dissection. 



In the mosquito (Plate XXVIII, fig. 3) the testes are small ovoid bodies, 

 with a slightly green tinge in the fresh state. The vasa deferentia which 



lead from them are extremely slender tubes of con- 



.... Culex and Tabanus 



siderable length ; each expands at the distal end to 



