1912] Richardson — Life-History of Corethra Albipcs Johannsen 201 



The labrum is a large papilliform organ with two groups of about 

 twenty stout hairs at the distal end, and a single bristle on either 

 side about one third the length of the labrum above the distal end. 

 Between the labrum and the mandibles and above the latter are 

 the paired fans, each composed of nine long coarse hairs. There 



Fig. 1. Antennae ot Corethra albipcs Johannsen. 



are from 18 to 22 such hairs on the fans of americana according to 

 Johannsen. The mandibles consist of a group of about four, 

 large, brown chitinized teeth, the last with a serrated posterior 

 margin; above the teeth and on the anterior surface of the man- 

 dibles are tw^o spines. The maxillae are fleshy lobes each with one 

 anterior long jointed appendage, one median short stout spine 

 and a smaller posterior spine. The labium possesses two short 

 spines of equal length. 



The two pairs of air sacs are situated in the thorax and in the 

 seventh abdominal segment respectively as in C. plumicornis 

 var. americana Johannsen. Their dorsal surface is covered by 

 large pigmented cells with large nuclei which appear as hyaline 

 spots in the darker medium. 



The caudal appendages are as follows: a ventral comb of 

 twenty long, plumose hairs; Johannsen gives twenty -five such 

 hairs for americana; four elongate blood-gills on the apex of the 

 caudal segment; above these four plumose apical hairs, the dorsal 

 pair longer than the ventral; about twelve short, apical hooks 

 situated between the ventral comb and the blood gills, each with 



