2l8 L. M. HICKERXELL. 



studied in sections. However, the general ground plan is soon 

 seen to be in no way different from that in the stages previously 

 described. 



The internal gland has the same structure here as it does in 

 the older nymph. In size, it is of course, smaller but sections 

 show identical parts in the two stages. 



The descending intestine and rectum have the same form and 

 arrangement in the 7 mm. and 14 mm. nymphs as they do in 

 the later stages. The diameter of the descending intestine is 

 very small. It runs close to the dorsal integument in some places 

 and might easily be missed in studying sections. The character- 

 istic coil (Fig. 2, kk) exhibits a convolution which is practically 

 the same as that described for the later stage. 



Examination of Figs. I and 2 makes it clear that there is no 

 great difference in the arrangement of the digestive organs of 

 the nymphal stages considered. It is also true that in the 2.\ 

 mm. nymph there is not enough difference in structure or ar- 

 rangement to warrant making a separate figure to represent con- 

 ditions there. This means that the plan of the digestive apparatus 

 is not altered practically throughout the entire underground 

 existence of the insect. The variation in the size of certain organs 

 at different periods in the life-history suggests either that the 

 nymph does not feed continuously or that there is a change in 

 the function of some of the organs as time goes on. The former 

 supposition is probably correct for it is known that these imma- 

 ture forms have alternate periods of feeding and resting. 



The ascending intestine is found in some sections to have its 

 epithelial lining made up of enormous cells filled with granules. 

 In other cases w r e have the condition represented in Fig. 4, at, 

 where the walls of this organ are thin and attenuated. These 

 variations probably represent different phases of functional ac- 

 tivity and are not to be interpreted, therefore, as indicating any 

 change in the plan of digestive activity. 



The complication of organs in the anterior region which has 

 been called the internal gland, arises at a time earlier than that 

 represented in the stages here described. Fig. 3, which is a 

 transverse section through the internal gland region of a 24 mm. 

 nymph, shows all the parts arranged in a manner similar to that 

 in the adult. In Fig. 5, which is a like section through the same 



