20 



0.9 mm in length by 0.6 mm in diameter, those of the male being slightly 

 smaller. Their shape has also considerably changed; they are now of 

 a regularly oval form, and are stoutest anteriorly. 



The cast skins (fig. 2, d) are pale yellowish, with the last three seg 

 ments yellowish-brown and the anal tube dark brown. They present 

 the following characters: 



The rostrum is very large, distinctly two-jointed, and situated at 

 about the middle of the body. The orifices of the stigmata are very 

 large and circular, their internal prolongation about twice the length 

 of their diameter, with the external half cylindrical constricted at the 

 inner end, while that part beyond the constriction is obconic or funnel 

 shaped and connected with tracheae, running parallel with the sides of 

 the body. On the under side of the abdomen and in front of the anal 

 tube maybe observed a median row of five large pores, and similar 

 pores, together with numerous smaller ones, on the upper side of the 



a c H 



Fig. 2.—Xylococcus betulce: a, first larva, male, female, ventral view; 6, antenna; c, tarsus; d, cast 

 skin of first larva — a and d much enlarged, b and c, more enlarged (original). 



two last segments and along the sides of the abdomen; there are also 

 numerous rows of minute sharp points on the dorsum of the six anterior 

 segments of the abdomen, and in addition a row of sparsely set short 

 and backward-directed spines, all of which arise from small tubercles. 

 The cephalic and thoracic segments appear to be smooth aud without 

 pores. There seems to be no appreciable difference between the sexes, 

 except that the male larva3 are slightly smaller. 



In fig. 3, a and b respectively, are shown enlarged ventral and 

 dorsal views of the end of the body of the female. At c, a stigma is 

 figured highly magnified. 



Female, second stage {fig. 6, a). — In this, as well as in all the following- 

 stages, except the last, the legs and antenme are completely lost. All 

 these stages are of an orange color, with the end of the body of a 

 lighter or darker brown ; the eyes are minute and blackish; their bodies 

 are ovoid, somewhat broadest anteriorly, quite flat or slightly convex, 

 smooth and shining, and without any apparent segmentation. The 



