METAZOA INSECTA. 457 



According to Comstock, whose natural classification of 

 the Lepidoptera we have adopted essentially, the Frenatae 

 which do not now possess a frenulum (some moths, all 

 skippers, and butterflies) have gradually lost it, owing 

 probably to the large development of the front edge of 

 the basal portion of the hind wing which fits under the 

 fore wings so closely that unity of action is made possible. 

 The frenulum, not needed, would gradually tend to disap- 

 pear. 1 



Frenatae. The larvae of the flannel moths of the 

 family Megalopygidae have seven pairs of prop-legs 

 besides the three pairs of thoracic legs (No. 1159, upper 

 left hand specimen of Megalopyge crispata}. They make 

 a trap-door cocoon (No. 1159, lower left hand specimen). 

 The adult (No. 1159, right hand specimen) is covered 

 with crinkly hair and hence the popular name. 



The Psychidae remind one of caddis-flies, since their 

 caterpillars make a bag and cover it with sticks (No. 1160, 

 Psyche pulld) which they carry about with them. The 

 adult (No. 1161, $) is one of the small moths. The 

 wingless female is specialized by reduction and is an illus- 

 tration of suppressed development. This reduction is 

 clearly shown in the evergreen bag-worm, Thyridopteryx 

 ephemeraeformis Haw. (PI. 1162, figs. 1-6). If the larva 

 (fig. T; fig. 2, in case or "bag") is to become a male 

 (according to Riley the caterpillars are all alike until the 

 pupal stage is reached, when the sexes are differentiated), 

 the development proceeds as in most Lepidopterous in- 



iDr. A. S. Packard (Mem. Nat. Acad. Sci., VII, Monograph i, 

 ^95, p- 57) objects to this division of the Lepidoptera into the 

 Jugatae and Frenatae on the ground that the characters are too 

 slight, considering that the structure of the mouth parts and more 

 especially the characters of the pupa are of fundamental importance 

 in working out the phylogeny of the group. 



For our .present purpose, however, the classification given by 

 Comstock is more simple and more in harmony with that of the 

 other orders of insects, while at the same time it is based on philo- 

 sophical reasoning. 



