602 ROBERT MATHESON 



The shedding of the pupal intima 



This occurs three to four days after pupation, and the changes 

 that have been going on up to this time become more intensive. 

 The epithelial cells retain their characteristic appearance. The 

 number of degenerating cells is rapidly decreasing, while there is 

 a marked increase in the number undergoing division. In any 

 cross section one can count from four to seven nuclei undergoing 

 mitosis. The dividing nuclei are not so numerous in the anterior 

 or posterior portions. The pupal intima now lies free within the 

 lumen. Between the cast intima and the epithelium one finds a 

 somewhat granular secretion filling up this area and so closing the 

 lumen (fig. 26, cj.m.). Owing to their great secretory activity 

 the cells are being rapidly reduced in size ; the vacuoles, now nearly 

 all at the tips of the cells, are smaller or frequently lacking; the 

 longitudinal folds are lacking except near the posterior end where 

 numerous small folds are being formed ; the intestine is somewhat 

 larger. The oesophageal valve is now reformed as it will appear 

 in the imago except for slight cellular changes. 



The beginnings of the imaginal intima now show their early 

 appearance. In figure 22, one observes near the inner surface of 

 the cells a row of very distinct, sharply staining, black dots, 

 underlying a granular layer which does not show very clearly in 

 the photograph. This is shown much better in figure 29, r, from 

 a pupa only forty-eight hours old, though it is not commonly seen 

 so early. This condition agrees with what Deegener ('08) con- 

 siders as the origin of the intima in the developing fore-gut of 

 Malacosoma castrensis. As the imaginal intima appears in this 

 place one seems forced to conclude that it is formed not only by 

 secretion but also by a direct transformation of the cells them- 

 selves. 



Formation of the imaginal epithelium 



The changes that occur after the shedding of the pupal intima 

 are not very considerable. The oesophageal valve remains practi- 

 cally the same as in the four-day-old pupa. In the region directly 

 cephalad of the valve the formation of longitudinal ridges con- 

 \ tinues to a marked degree. This decuples only a short distance, 



