36 THE EARLY STAGES OF TABANID^ 



study of this region shows that the two cysts are not completely sepa- 

 rated and, on the contrary, communicate with one another in their 

 axial region; in other words, the septum which separates them is 

 incomplete. The tubular region which prolongs the posterior cyst 

 begins towards the middle of the segment next to the last and opens 

 in the median line not far from the openings of the two tracheal tubes. 

 This tubular region is, consequently, about as long as the dilated por- 

 tion of the organ. The fundus of the sac, that is its anterior region, 

 has thicker walls than any other part. There is in this region a 

 cellular mass similar to that described by Henneguy in the organ of 

 the undetermined larva which he examined. 



The ink-black bodies can be found, according to Lecaillon, in both 

 capsules and in the tubular portion. The first capsule always con- 

 tains two which are situated anteriorly, one to the right, the other to 

 the left of the median line. By carefully examining their arrangement 

 it is found that they are attached to the cellular mass at the fundus 

 of the cyst, each by a small pedicel, as has been described by Graber 

 and by Henneguy, whose observations are confirmed by Lecaillon. 

 These pedicels do not show on Lecaillon's figures, which, as he says, 

 were drawn from living larvae under conditions when the details were 

 not clearly visible.^ The second capsule contains sometimes also two 

 of the black bodies, arranged as in the first capsule, but often it 

 does not contain any of them. 



The tubular region often contains no black bodies. But frequently 

 and especially in older larvae, it almost always contains a varying 

 number. The maximum number which Lecaillon found was sLx, but 

 there may be only five, four, three, or two, even in larvas of the same 

 age and living under the same conditions. As the caliber of the tubu- 

 lar region is narrow, the black globules are placed here in a length- 

 wise row, and not in pairs placed transversely, as in the capsules. 



As Lecaillon wished to ascertain whether the black bodies could 

 eventually be expelled to the exterior, a larva which had six globules 

 in the tubular portion of the organ was placed under observation. 

 Eight days afterwards Lecaillon found that the tube contained only 



^ I found that living tabanid larvae up to 15 mm. in size can be examined by 

 means of a compound microscope, without suffering injury from the pressure 

 necessary to hold them in place. 



