ABOUT CATERPILLARS 205 



which are still enigmas. One is the purpose or 

 cause of the excessively constricted neck of the 

 caterpillars of Hesperidae, a universal character- 

 istic and one that is widely different from the fre- 

 quent enlargement of this segment, as we find it in 

 the Papilioninae, and to a much greater extent in 

 the Lycaeninae. Another is the curious swollen 

 vesicle which hangs like a bag, a blunt, conical, 

 or transverse structure below the first thoracic seg- 

 ment in advance of the legs. Various suggestions 

 have been made with regard to this. It is a very 

 common occurrence, perhaps not universal, with 

 caterpillars, but very much more higlily developed 

 in some than in others. In those in which it is 

 most highly developed, we have found no habit or 

 peculiarity which would explain its purpose. It is 

 ordinarily covered with gritty tubercles of a spe- 

 cial structure, but as far as I have been able to see, 

 contains no openings whatever. Many other singu- 

 lar things about caterpillars needing explanation 

 could be given, especially as regards their color- 

 ing, but these will suffice to show that there is 

 yet a wide field open, even among our commonest 

 forms. 



