GLOSSINA PALPALIS: REPRODUCTION 385 



above is very peculiar and interesting. Several observers have noticed 

 that those which rest on the outskirts of the gite, at some little distance 

 from the water, are much the most active, and immediately attack the 

 first host which comes their way, taking a full meal at the first 

 opportunity ; those which are in the interior, near the water, are 

 found resting on stones on the river bank, or on trees thrown across 

 the water; they make no attempt to bite and merely rest in the sun as 

 near the water as possible, flying up when disturbed, but returning 

 with a remarkable persistence to the same place. Many of these in 

 the interior of the gite are males. 



The length of flight of palpalis under ordinary circumstances is 

 probably not great, as they show no tendency to leave their haunts, 

 but rather wait there till their prey comes to them. There seems 

 to be no doubt, however, that they will occasionally fly considerable 

 distances over water to reach boats passing along the rivers, and 

 at the time of their migration from the temporary gites to the permanent 

 water courses long distances may be covered, in this case by a series 

 of flights. They frequently follow native carriers for some distance 

 away (rom water. 



Reproduction, in all the species of GJossina, is larviparous in type. 

 The reproductive tract of the female has already been described in 



Chapter II, where it was explained that the two 



c u 4- i c j u ^u Reproduction 



ovaries function alternately, first one and then the 



other producing an ovum, and that the ovum passes down into the 

 uterus, where the larva hatches and completes its growth. It is neces- 

 sary to consider the phenomena of reproduction in some detail ; as before, 

 the main source of our information is the extremely interesting thesis 

 of Roubaud. 



The passage of the mature egg to the uterus, according to Roubaud, is 

 determined by a special mechanism, possibly under the control of the 



nervous system of the fly, which under certain circum- 



, . , ,, ,. , , , Descent of the egg 



stances may bring about the retention of the egg in the 



ovary, even when mature. One of the determining conditions is the 

 presence of spermatozoa as a result of copulation ; if copulation has not 

 taken place, as in female flies kept apart from the male from the time 

 they hatch out, a mature egg is found engaged in the upper end of the 

 common oviduct, but never actually in the uterus ; the egg which should 

 follow this may be in a much more advanced state of development than 

 would be found in the normal condition. The reason for this retention 

 is that the aperture through, which the spermatozoa penetrate is-pkced- 

 49 



