212 ANIMAL LIFE AND HUMAN PROGRESS 



is pale yellow, and the terminal segment is furnished with a 

 pair of intensely black and somewhat hemispherical protuber- 

 ances (the " tumid lips " of various authors, " ballonnets " 

 of Roubaud), with a deep, cup-shaped pit or cavity between 

 them. The paired stigmata of the respiratory organs open 

 into the pit, and it has been held, until quite recently, that 

 the protuberances or lobes function as a protection for the 

 openings, thus forming a kind of air-chamber favourable to 

 gaseous exchange during the intra-uterine life of the larva. 

 Recent investigations x have shown that the lobes them- 

 selves are also provided with innumerable " air-holes " 

 (about 500 pairs), and that these unique structures func- 

 tion only while the larva is maturing within the body of 

 the parent. 



Immediately after birth the larva buries itself in the earth 

 or humus and rapidly undergoes its final change into the 

 nymph or pupal stage. In this case the old larval skin is 

 not cast off but is retained practically intact ; it hardens 

 rapidly and forms a protection or covering (puparium) for 

 the enclosed pupa or nymph. The fly matures in about three 

 weeks, and, in order to escape, breaks off the anterior end of 

 the puparium by means of the frontal sac in a way precisely 

 similar to that of the house-fly and other members of the 

 Diptera Cylorrhapha. 



In the year 1903, when Mr. E. E. Austen published his 

 classical monograph of the tsetse-flies, only seven species were 

 known to science. Since that date, however, nine additional 

 species and four or five colour- varieties have been described, 

 and it is highly probable that other species await the dis- 

 coverer in the African continent. 



These insects may be divided into three main groups, 

 each group being clearly defined by the morphological char- 

 acters of the male genital armature. In the Glossina fusca 

 group the superior claspers are quite free ; in the second group, 

 of which G. palpalis may be taken as a type, the superior 

 claspers are united by a membrane, but the tips of the claspers 

 are free and widely separated ; in Group III., G. morsitans, the 

 1 Annals of Tropical Medicine and Parasitology , vol. xii. p. 93. 



