414 RICHARD EVANS. 



fig. 30j which represents an older stage, the difference is not 

 so marked, as the cells on the upper aspect have in some cases 

 made their way to the surface, and in fig. 31 the epithelial 

 membrane of the upper surface is as complete as that of the 

 lower. 



In the interior of the pupa the cells with granular nuclei 

 continue to line the persistent larval cavity, which in some 

 larvse may be of great size (figs. 29 and 30). The cells with 

 granular nuclei, situated in the solid part of the inner mass, 

 flatten out to form the -lining of the exhalant canal system. 

 The canals, which are short at this stage when they exist, may 

 be seen to communicate on the one hand with the larval 

 cavity, and on the other with the cavity of the flagellated 

 chambers. These connections explain why some observers 

 have made the mistake of describing the flagellated chambers 

 as developed from the cells of the inner mass at the blind 

 ends of outgrowths from the flattened layer of cells lining the 

 larval cavity, i.e. from the so-called '^entoderm." 



The special features of the pupa derived from the larva 

 described above as type C may be summed up as follows : 



1. The flagellated cells pass in at different rates from the 

 lower and upper surfaces, and consequently the flattened epi- 

 thelium forms much more slowly on the latter than on the 

 former. The difference in question is much more marked in 

 this pupa than in the one derived from the larva described as 

 type D. 



2. Flagellated chambers are always present, appearing in 

 section as rings. In many cases the individual cells are pro- 

 vided with a collar and a flagellum even at the time of fixation. 



3. The flagellated cells, after passing into the interior, take 

 part in the formation of plasmodial aggregations, from which 

 they later emancipate themselves and give rise to flagel- 

 lated chambers, the cells of which for a time can be distin- 

 guished from the cells of the chambers derived from the 

 " inner mass " by their nuclear and other characters (figs. 

 28, 31). 



4. The canal systems appear as early as the time of fixation. 



