142 THE EARLY STAGES OF TABANID^ 



thick, and impermeable integument. In acetic sublimate, at a tem- 

 perature of 24°, the larvae remain alive for more than half an hour. 

 It may be mentioned that many dipterous larvae behave in this rela- 

 tion exactly like the larvee of tabanids. 



Lecaillon has again tried to rear larvae of this species which had 

 hatched on June 27, 1905. He found that they succeed best in moist 

 ground. In February, 1906, a rather large number of these larvae 

 were still alive; they had grown comparatively little, measuring only 

 7 or 8 mm. in length, against 2 or 3 mm. at the time of their birth. 

 Some lived for a year without having reached a much greater size 

 than this. Some of the larvae were still found alive in July, 1906. 



Under the conditions mentioned, the intestinal tract of the larvae 

 almost always contains particles of soil, giving them a blackish color. 



From these observations it is probable that in Tahanus quatuorno- 

 tatiis the duration of the larval stage is more than one year. However, 

 Lecaillon believes that this need not necessarily be, as it is apparent 

 that the larvae when kept in moist earth do not find exactly the con- 

 ditions under which they live in nature. Their growth is consequently 

 much diminished and cannot be compared with normal growth. 

 This subject, however, requires further investigation. 



The chitinous cuticle of the larva was also studied by Lecaillon 

 (1906). It is thick and resistant, as genierally in dipterous larvae. 

 Its thickness in a larva of 630 ix in diameter being about 17 ^t. This 

 resistant and impermeable covering protects the larva efficiently. 

 It may be left in the water, for instance, for several hours without 

 being appreciably injured. It can be left, on the other hand, in dried 

 soil for a considerable time without being killed. If one wishes to 

 fix the larvae in toto, even in the case of very small larvae, great diffi- 

 culties are encountered because of the impermeability of the chitinous 

 membrane. 



The free surface of the chitinous layer appears to the unaided eye 

 to be smooth and devoid of hairs. But with a lens it is found that it 

 presents numerous longitudinal parallel ridges and numerous hairs of 

 reduced length. This characteristic has been found to be a general 

 feature of tabanid larvae, and the examination of the striae can fur- 

 nish the means to distinguish the genera and species. 



