744 CHARLES PAUL ALEXANDER 



The type specimen should, of course, be selected only when there is 

 absolute certainty of the identification, and in most cases this determination 

 can be made only by rearing the species. After the species has been reared 

 (this should be done many times, if possible, in order to check up the 

 identity) , a good representative specimen may be chosen as the type of the 

 stage. In the cases in which the species is known only from a single 

 specimen, the nepionotype may be the larval skin, the neanotype the 

 pupal skin. The remaining specimens of the original series become para- 

 types. The types of the immature stages possess fully the value of the 

 type of the adult and should be as carefully preserved. The types herein 

 designated are in the collection of the writer. They are preserved in 

 alcohol, but the larval heads of most species have been removed, treated 

 with caustic potash, and mounted in balsam. 



EXTERNAL MORPHOLOGY 



The larvae and the pupae of crane-flies show considerable diversity 

 in their general form. The fundamental plan of structure remains much 

 the same thruout the group, but the details are widely different and furnish 

 the characters in use for the separation of the various tribes and lesser 

 divisions. 



The immature stages of crane-flies have evolved more rapidly than 

 have the adult flies, and in many features they show a greater specialization. 

 The head capsule of the larva seems to be the most constant feature, 

 the same fundamental type of structure recurring in the generalized 

 members of all the various groups, indicating a close phylogenetic relation- 

 ship. On the other hand, the respiratory organs of both the larvae and 

 the pupae vary greatly in the different species and are obviously molded 

 by habitat. The often-repeated statement that the inside of an organism 

 shows what -it is, while the outside shows where it has been, is well illus- 

 trated here. 



The larva 

 General features 



The form of the larval body is, as a rule, moderately elongated and 

 usually terete. The head is eucephalous and non-retractile in the three 

 families Tanyderidae, Ptychopteridae, and Rhyphidae. It is incomplete 

 and more or less retractile in all the species of Tipulidae. The body 

 is shortest in the more generalized forms, becoming greatly elongated 



