BIORHIZA APTERA. 99 



Average dimensions of a mature specimen. — Oue larval 

 cell : Height, 8 mm. ; girtli, 30 mm. 



May be sought during any month of the year. 



Growth is complete by the end of October. 



The typical condition of the gall is unilocular and unilarval. 



The larva pupates in the gall. The imago emerges during the 

 winter and the spring. 



Parasites, Nos. 15, 175. 



Alternate sexual generation : Teras terminalis, Fabr. 



" The time given by different authorities for the 

 appearance of the flies varies, some having found them 

 in November and some in March ; according to my 

 own observations the latter date must be considered 

 exceptional, at least in this place (Schleswig). I have 

 for many years found the flies regularly in the end of 

 December and beginning of January" (Adler, 'Alter- 

 nating Generations,' p. 71). 



This gall appears to have been well known in the 

 south of England prior to the year 1 874. But it had 

 only been o1")served on the roots of oak trees that had 

 been blown down by gales, and not as the result of 

 entomological research. It occurs on the subterranean 

 roots only ; on the largest and thickest, as well as on 

 the most slender, but with greatest frequency on those 

 varying in dimensions from that of a quill to that of a 

 lead pencil. 



It is seldom solitary, but when so the size ranges 

 from 5 mm. to about 15 mm. in diameter, and the 

 shape is more or less globular. 



The general condition of growth is gregarious, and 

 in conglomerated clusters of considerable numbers ; 

 the overcrowding in some masses being so great that 

 distortion and fantastic shapes are the result. Some 

 clusters reseml)le the gall of Apliilotlwix radicu, but 

 may be easily distinguished from that species by {a) 

 the outline of the cluster showing each separate larval 

 chamber; (li) each larval chamber, although attached 

 to those next it, may be separated without injury ; or 

 (c) by making a transverse section, when it will be 



