hisects and Pains I tic Diseases. 27 



It measured 2.376 niin. in length by about 0.05 inm, in width 

 at the base of the oesophagus. The cylindrical pharnyx -was- 

 0.0495 mm. in length. The nerve ring and the ba^e of the oeso- 

 phagus were about 0.132 nnu. and 0.92 nun. respectively from the- 

 anterior end of the l;ody. The anterior end of the oesophagus 

 measured about 0.0115 mm. across, and increased in width some- 

 what sharply about 0.208 )nm. from the anterior end of the bod}^ 

 to a maximum width, at the base of the oesophagus, of 0.039 mm. 

 The tail tapers evenly and gradually to the rounded tip, which is 

 covered with small spines (Fig. 16). Similar larvae are co-nnnonlj^ 

 found in the head, thorax, and abdomen of flies, and not infre- 

 quently within cysts in the last position. 



The length of larval H. muscae in the final stage found by the- 

 writer in laboratory-bred flies ranges from 2.145 mm. to 2.541 mm., 

 while the range for what are believed to be Habronema muscae (three 

 specimens) found in naturally infected cauglit flies is 2. 178 mm. 

 to 2.244 mm. The range given by Ransom (1913, 21) for the Ijitrer 

 is 2.6 nun. to 3.2 mm., the minimum being only 0.04 mm. less 

 than the maximum length known to the writer to be attained by 

 Habronema in the fly. This specimen from a culture artificiallv 

 infected with embryonic H. muscae (?) was found (November lOth) 

 in a fly five days after its emergence from the pupa. 



All stages of the parasite excepting the earliest stage found in 

 the fly larva (see Fig. 4) are knoAvn to the Avriter to sometimes- 

 occur in cysts. 



Encystment is a condition believed to be assumed by the larval 

 parasite when about to enter a resting period, and not a necessarv 

 condition in the process of development. 



It has not been considered necessary at the present stage of this 

 investigation to discuss in detail the minute internal developmental 

 changes which take place in tlie embryonic and larval stages other 

 than as indicated by the variations in the relative lengths and 

 diameters of the parts shown in Table No. 2. The general structure' 

 of each stage is shown by the figures and the comments thereon, in 

 this section the term " stage " being employed in a wide sense to- 

 indicate obvious steps in tlie process of development. 



Summary and Discussion. 



As will l>e seen, this investigation into the life-history of 

 Habronema muscae is practically a confirmation and extension of 

 the observations by Ransom, to which frequent reference has been 



