OLFACTORY SENSE OF THE HONEY BEE 325 



advanced pupae the hypodermis is still thinner and seems to be 

 entirel}^ absent at places. In the legs of younger pupae it is 

 much thicker. Beneath the pores in the wings the hypodermis 

 is much thicker than elsewhere (fig. 19, Hijp). In none of these 

 sections of bees older than the 16-day-old pupae was it possible 

 to distinguish a true basal membrane of the hypodermis, although 

 it is very probable that the inner hypodermal wall (fig. 17, HypW) 

 is the remains of this membrane. In younger stages of the pupae 

 this membrane is present. 



In the 16-day-old worker pupae neither pores nor sense cells 

 are found. At this age many large and deeply staining nuclei 

 occur in the hypodermis where the sense cells later appear. All 

 stages in the formation of hairs may be found. The muscles 

 are not yet completely differentiated and appear as more or 

 less indefinite masses. 



In all the sections of legs from the 17-day-old worker pupae, 

 pores are always found, and sense cells are usually present. The 

 chitin and most of the hairs are now fully developed. The hypo- 

 dermis is much thinner than in the 16-day-old pupa^, and in 

 fact most of the various structures are fully differentiated. Thus 

 it is evident that between the sixteenth and seventeenth days 

 there is a rapid change in the various structures and that at 

 this time these sense organs make their appearance. Very often 

 in this and later stages the inner hypodermal wall (fig. 19, 

 HypCW) is absent beneath the pores. In such cases it is some- 

 times impossible to distinguish hypodermal nuclei from sense cell 

 nuclei. The sense cells, therefore, are derived from the hypoder- 

 mis and are nothing less than modified hypodermal cells that 

 have assumed a difTerent function. In regard to the formation 

 of the pores and cones nothing can be stated because this phase 

 of the subject was not studied. 



In sections from the more advanced pupae and in those from 

 the adult bees, pores and sense cells are always present. Very 

 often in sections of legs from pupae 17 days old a large, dark 

 nucleus (fig. 19, HypNuc') is present beneath a hair. At first 

 it is easily mistaken for a sense cell belonging to the hair, but a 

 careful investigation always shows that it is the hair mother cell 



