748 CHARLES PAUL ALEXANDER 



Anal gills. In the Ptychopteridae and in the Tanyderidae there is 

 but a single pair of anal tracheal gills. In the former these are very small 

 and are cylindrical, in the latter they are large, branched, fanlike struc- 

 tures. In the Tipulidae the anal gills number from four in most Lim- 

 nobiinae to six or eight in the Tipulinae. The increase in number is brought 

 about by a division of the original gill of each side. In generalized forms, 

 as Antocha, Pedicia, and others, the anal gills are constricted into segments, 

 the apical ones being more or less telescopic into the preceding ones. As 

 a rule the anal gills are entirely or almost entirely retractile within the 

 body. 



In the Tipulinae the gills vary with the genera, being blunt and con- 

 structed for propulsion in the wood-inhabiting species, such as those of 

 Ctenophora, Tanyptera, Tipula, and other genera. In the semi-aquatic 

 species of Tipula the number of gills varies from four to eight. In the 

 latter case each of the four principal gills is deeply bifid and the gills are 

 arranged transversely, as in T. ignobilis] in species with six gills the posterior 

 branches of the posterior gills are atrophied as a rule; in other species, 

 which have but four gills, the four anterior branches are preserved, the 

 posterior pair being usually atrophied. In Longurio and Aeshnasoma 

 the four anal gills are pinnately branched, each with about six lateral 

 branches. A similar condition is found in the Tanyderidae. 



The head 



The primitive crane-fly head was undoubtedly of the eucephalous, 

 non-retractile type, as found in the Ptychopteridae, the Rhyphidae, and 

 other families. The retracted head capsule of the Tipulidae is a derived 

 condition. 



The massive, compact capsule is found in all of the lower groups of the 

 three subfamilies of the Tipulidae. Such a head is easily derivable from 

 the condition in the Rhyphidae or in the Tanyderidae, for instance. The 

 dorsal median sclerite, the prefrons, is almost as large and conspicuous 

 in Ula as in the eucephalous families. The lateral plates that constitute 

 the capsule are shaped like a mussel in the generalized groups, with the 

 posterior incisions shallow. In the more specialized forms, with the 

 capsule greatly dissected, the two plates of either side are entirely sepa- 

 rated the innermost, next to the prefrons, being the internal-lateral 

 of De Meijere, and the outermost being his external-lateral. The prefrons 



