SURROUNDINGS OF GROWING INSECTS 219 



numbers from August until January in the gullets of 

 slaughtered cattle, embedded in the sub-mucous coat. They 

 are now in the second stage (from 5 to 12 mm. long), 1 with 

 the spiny armature on the segments hardly perceptible, except 

 for a few short black spines near the tail-spiracles (Fig. 109 e). 

 From December onwards they begin to appear, still in the 



A Sp 



P. Sp. 



FIG. 109. ox WARBLE-FLY (Hypoderma bovis). 

 x 2\. b, full-grown (fourth stage) larva (dorsal view). x 2. 



a, female, x ai. b, full-grown (fourth stage) larva (dorsal view). < 2. c, egg. x 20. 

 d, empty puparium (lid broken away). x ij. e, second stage maggot (from gullet of cattle). 

 X 5. /, first stage maggot (H, mouth-hooks ; M, median spine ; Ph, pharyiigeal sclerites ; 

 A. Sp, anterior, and P. S/>, posterior spiracles). x 70. a d, from Theobald, "Report 

 on Econ. Zool ". I ; /, after Carpenter and Hewitt, Proc. K. Dublin Soc. XIV. 



second stage, beneath the skin of the back, having migrated 

 by way of the diaphragm, or the neck and back-muscles, and 

 the vertebral canal. The mouth-armature of the second 

 stage larva is fairly strong, and is doubtless serviceable in 

 biting a passage through the tissues. Soon after arriving 

 beneath the skin of the back, the maggot assumes its third 

 condition ; there are now distinct rows of spines on the ventral 



1 E. W. Laake (Journ. Agric. Res. XXI No. 7, 1921) states that two 

 distinct instars are inc'uded in this " second stage." 



