50 EXPERIMENTS WITH CERTAIN DIPTERA. 



The tail was dra\vn out into a point situated GO /< from 

 the anus. At this stage the transverse annulations were 

 only faintly marked. A gradual increase in size takes 

 place (figs. 10, 11), the fully developed worm measuring 

 from 2 8 to 3.4 mm. in length. This stage (figs. 12, 14, 15) 

 is usuall}' found in the head and proboscis. The mouth 

 is surrounded bj' several small papillae and leads into the 

 pharynx which now measures 25 ji in depth hx 15 fi in 

 width (fig. 14). The oesojohagus gradually increases in 

 width from 20 [x to 35 /< at the oesophageo-intestinal 

 junction which is situated 230 /; from the mouth. The 

 nerve ring encircles the oesophagus at a distance of 160 ^ 

 from the anterior end. The long straight intestine leads 

 into the rectum, which is 180 //. in length by 40 [a in the 

 A\-idest part. The anus, now open, is situated 85 fx from the 

 tip of the tail. Three small papillae are present on the tail, 

 one terminal and two situated on either side a short distance 

 in front of it. The worm is thick anteriorly tapering off 

 towards the posterior end. The breadth at the base of the 

 oesophagus is 95 ji, and at the anus 45 ^<. At this stage the 

 transverse annulations are well marked in the anterior 

 portion of the worm, being most prominent about the 

 junction of the oesophagus and intestine. The}^ are situated 

 from 5 to 7 [.i apart. Towards the posterior end they 

 become fainter and cannot always be made out in the 

 anal region. In one specimen the annulations were rounded 

 off, giN'ing a different effect from that shown in fig. 14. 

 In other respects the worm was a typical Agamosjnrura 

 muscarum. 



The characters of the parasite suggest that it repre- 

 sents the larval stage of one of the Spimroidea, perhaps 

 of the Sjjiruridoe, hence the larval collective generic design- 

 ation. The sjoecific name is given owing to the comparative 

 frequency of the occurrence of the worm in many local 

 Muscidse. 



Attempts were made to trace the origin of the nematode 

 by breeding out flies from various materials. 



The results were as follows. 

 M. fergusoni. 



(1) Cow dung. Two hundred and seventy-eight speci- 

 mens (including a few pupse) bred from cow dung from. 



