42 EXPERIMENTS WITH CERTAIN DIPTERA. 



counting them. The enormous number of larvae does not 

 seem to inconvenience a fly greatly since the individual 

 referred to above had lived for a fortnight in capti^^ty in 

 apparent good health prior to dissection. 



Agamofilaria tabanicola n.sp. 



■ (Text-figures 1-8). 



The microfilariae taken up with the blood or lymph 

 of their vertebrate host by the March fly leave the gut and 

 encyst in the fatty tissue in the abdomen of the insect, the 

 earliest stages found being in this region. Larvae ranging 

 in length from 150 ju to 1250 ju have been met with in this 

 situation (figs. 1-3) The final stage in the fly has been 

 found free in the abdomen, thorax, head and proboscis 

 (fig. 4). The worms seem to be attracted to the proboscis 

 and in a heavily infected fly they are seen to be congregated 

 in and around the base of that organ. In one instance after 

 the proboscis was severed from the head in normal saline, 

 two larvae emerged for about half their length from the 

 apparently uninjured tip of the proboscis. 



The youngest worms seen measured 150 /^-260 /j in length 

 with a maximum width of 21-30 ju (fig. 5). There is a 

 definite cuticle ; the oesophagus is clearly marked off from 

 the intestine and the anus lies at about 25 ^ from the 

 pointed posterior end. The nerve ring lies at about 50 fj, 

 from the anterior end (stage 1). 



As development proceeds (stages 2 and 3) there is a 

 progressive lengthening but only a slight increase in width ; 

 in fact the final stage is thinner at either end (though not 

 in the mid region) both relatively and absolutely than in 

 the earlier stages. In th? final stage (stage 4) the worms 

 measure from 1.93-2.4 mm. with a maximum width of 

 35 to 40 jii. The nerve ring lies at 115-120// from the 

 anterior end. The oesophago-intestinal unction, which 

 is so well marked in the earlier forms, becomes gradually 

 less distinct and cannot be made out in the final stage. 

 The intestine is a long narrow tube and is somewhat dilated 

 to form a rectum. The anus lies at about 40 fi from the 

 tip of the tail which is bhmtly rounded, though at the tip 

 of the tail the cuticle is drawn out into a little point giving 

 a characteristic appearance (fig. 8). There is a clear cuticle 

 1 /« in width, internal to which is the body wall from which 



