22 



Female, fourth stage {fig. 6, c). — Length 4 mm to 5 mm by about 2 mm in 

 diameter anteriorly. In the cast skin of this final larva the surface is 

 again densely and distinctly granulated, especially so on the last three 

 segments, which are now of a rather dark brownish-yellow color. The 

 pores have become still more numerous and are arranged in irregular 



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Pig. 5.—Xylococcus betulce: a. Ventral view of end of body of third stage at left. b. Dorsal view of 

 end of body of fourth stage at right — both much enlarged (original). 



bauds across the abdominal segments, becoming most dense and more 

 irregular on the three last segments; some of the pores around the 

 margin and end of the body are of complex structure; a pair of large 

 pores being surrounded by a ring composed of numerous minute pores. 



Fig. 6. — Xylococcus betulce: a, female, second stage; b, female, third stage; c, female, fourth stage; d, 

 anal tube showing internal structure ; e, compound and simple pores of end of body ; /, stigmatal 

 tubes and trachea? ; g, bit of same more enlarged— a, b, c, greatly enlarged ; d, /, more enlarged ; e, g, 

 still more enlarged (original). 



Similar compound pores were also observed in the second and third 

 stage. The stigmatal tubes are now about one-third longer than in 

 the third stage, while in the constriction there are from two to three 

 rows of pores. There now appears, placed medio- veutrally in the region 



