XVI] 



REPRODUCTION 



267 



The pregnant flies are liable to certain accidents of gestation, 

 for in captivity they frequently abort after being disturbed. 

 Sometimes the larva pupates whilst still within the uterus, 

 and in this case both the mother and its offspring invariably 

 perish, as the former is unable to feed and the latter cannot 

 emerge from the pupal case. A high degree of humidity is 

 very unfavourable to reproduetion, for Roubaud noticed that 

 when flies were exposed to a saturated atmosphere they either 

 aborted or did not develop larvae. These results would explain 

 why the females sometimes avoid the immediate neighbourhood 

 of water, whereas the males generally seek the damp places 

 where they require less food. The effect of this difference is 

 to cause that separation of the sexes of the flies, that has been 

 noticed by many observers. 



Fig. 70. Freshly laid larva of Glossina palpalis shewing the changes in the 

 body form. (After Roubaud.) 



When the larva is born it is a white cylindrical maggot, 

 with two black protuberances at its posterior extremity. 

 Its dimensions vary from 7 to 7*4 mm. in length by 2'8 to 

 3-5 mm. in diameter. At first the larva is very active, presenting* 

 curious alternate contractions and expansions of its body 

 (Fig. 70) causing it to assume very varied forms. These 

 movements enable the larva to bore its way into any fissures 

 or loose soil, and are peculiar to the members of the genus 

 Glossina. In loose sand the larva usually comes to rest at a 

 depth of about half an inch to an inch and then pupates. The 

 duration of the free larval stage does not exceed an hour to 



