H. M. Morris 105 



The peritrophic membrane is very common in Diptera, its length 

 varying considerably. In this larva as in many others the membrane 

 appears to arise from the anterior end of the cardia. 



In the general features of its morphology the larva of Bibio Johannis 

 bears a closer resemblance to the larvae of the Mycetophilidae than to 

 any other group. This resemblance appears to be due to the fact that 

 the two families are phylogenetically closely related. The possibility, 

 however, that certain of the characters may be the result of convergence 

 due to similarity of habitat must not be overlooked. 



6. THE PUPA. 



The larvae pupated on March 25th, the pupa being formed in an oval 

 cell of soil, the last larval skin being in the cell with the pupa. The cell 

 was considerably larger than the pupa, and quite smooth, and looked as 

 if it had been formed by the larva pressing outwards in all directions. 



The pupa is 7 to 8 mm. long, about 2 mm. broad across the thorax 

 and 1-3 to 1-5 mm. broad across the abdomen. 



The cuticle is smooth and white at first, but soon appears darker as 

 the parts of the imago darken and show through owing to the trans- 

 parency of the cuticle. The abdomen throughout is light in colour, as 

 the abdomen of the imago does not darken completely until after it has 

 emerged. 



The pupa of the female is distinctly larger than that of the male 

 particularly in the width of the abdomen. 



The head is flat below and is pressed down on to the prothorax. The 

 antenna cases are short and extend little more than half way across the 

 eyes. On the anterior end of the head is a stout process directed for- 

 wards, which covers the ocelli of the imago. The cases of the mouth- 

 parts are distinct. The thorax is short and thick, and the mesothorax 

 is considerably the largest segment. 



The leg-cases lie side by side, touching those of the other side in the 

 median dorsal line, and extend to about the middle of the first abdominal 

 segment. The cases- of the first pair of legs are wholly visible, those of 

 the second pair almost so, while only the extremities of the third pair are 

 left in sight. The remainder is covered by the wing-cases, which do 

 not quite meet and extend a little farther back than the leg-cases 

 (Plate II, fig. 3). 



Dorsally there is a slight ridge running from the posterior edge of the 

 mesothorax to the process on the head, and along this ridge the cuticle 

 splits for the imago to emerge (Plate II, fig. 2). 



