21 



in length 



fully grown larvae of the second stage measure about 1.5 

 by 0.9 ,um in diameter. 



The cast skin is almost colorless, except the last three or four seg- 

 ments of the abdomen, which are pale yellowish-brown, the anal tube 

 being darkest. The sur 

 face of the body is densely 

 and finely granulated, the 

 granulation being some- 

 what coarsest around the 

 tube. See fig. 4. There 

 are also small pores scat- 

 tered over the body, inter- 

 mixed with a few larger 

 ones on the last four seg- 

 ments, which bear also a 

 f e w backward - directed 

 spines. The internal stig- 

 matal tubes are now three 

 times the length of those 

 in the first stage; the out- 

 er two-thirds or more is 

 cylindrical and finely and 

 densely annulated; the 

 inner end of the tube is 

 bell- shaped, and in the con- 

 striction or neck of the 

 tube may be observed a 

 transverse row of large 



pores; the stigmatal tube is connected with the trachea? by a rather 

 long, annulated and bifurcate duct, of which one branch is longer than 

 the other. 



Female, third stage (fig. 6, b). — The mature larva of this form meas- 

 ures about 0.2 ,n,n in length by 1.4 mm in diameter, 

 X*\ and is very similar in appearance to the previ- 



ous stage. 



The cast skin is also colorless, except the two 

 last segments, wbich are pale brownish-yellow. 

 The pores are of two sizes and very numerous 

 on the abdomen and also around the margins 

 of the cephalic and thoracic segments. The 

 surface appears to be smooth and without 

 granulation s, except on the last two segments, 

 which bear also a number of stout spines each side of the anal tube. 

 (See fig. 5.) The stigmatal tubes are similar to those in the previous 

 stage, except that they are longer, and there are now two rows of pores 

 in the constriction or neck. 



Fig. 3. — Xylococcus betulce: a, ventral view of end of body of 

 female: 6, dorsal view of same ; c, stigma, all much enlarged 

 (original). 



Fig. 4. — Xylococcus betulce: 

 dorsal view of end of body of 

 second stage— much enlarged 

 (original). 



