1913] Wing Veins of Membracidce 75 



According to this theory the knowledge of homologies is 

 dependent upon two methods of investigation. First, the 

 ontogeny of the wing of the individual, as based on the study 

 of the tracheation of nymphal. wings traced through their 

 successive stages of development, and second, the study of the 

 wdngs of adults worked out by careful comparison with forms 

 representing known types of venation. Of these two methods, 

 the former has been the one used almost entirely and the second 

 has been resorted to only for those forms for which the nymphs 

 were not available. Since, however, the venation of the 

 Membracidae is comparatively uniform, the determination of 

 homologies, after the tracheation of the nymphs of the more 

 prominent types has been ascertained, has proven a relatively 

 simple matter. 



TECHNIQUE. 



The laboratory methods followed have been in the main 

 those outlined in the "Wings of Insects"^ with such modifica- 

 tions as have been suggested by the condition and shape of the 

 individual wings under consideration. 



The wings were dissected from nymphs of various stages of 

 development, but it was found that in most cases the last two 

 instars showed best the features desired. In these two instars 

 the nymphal wings may be pulled out of the wing-pads and are 

 thus more easily studied. In the earlier stages, and in all of 

 the stages of some of the smaller species, e. g. Vanduzea arquata 

 or Micrutalis calva, it is difficult to remove the wing from the 

 pad without disturbing the position of the tracheae, and in these 

 cases it is necessary to photograph through the pad membrane. 

 The wings were carefully dissected out, together with a portion 

 of the thorax to show the basal tracheation, and mounted at 

 once. It was found that fresh material gave much better 

 results than that which had been preserved, even for a short 

 time, in formol or alcohol. In many cases, several hundred 

 dissections were made for the verification of some particular 

 point in question. The greatest difficulty was to preserve the 

 tracheae for a sufficient length of time to secure photomicro- 

 graphs or careful drawings, since the tracheae fill in a very short 

 time with the mounting media and are then invisible. Moreover, 



3. American Naturalist, Vol. XXXII, p. 45. 



