14 C. HERBERT HURST. 



The five Malpighian cceca open into the anterior end of the 

 intestine. They are nearly cylindrical bodies of an intense white 

 colour ; their closed ends lie in the seventh or eighth segment, and 

 measure about 0"13 mm. in diameter. They run forwards, almost 

 straight, to near the anterior end of the fourth segment, and then 

 backwards to their point of opening into the intestine immediately 

 behind the constriction dividing the latter from the stomach. 

 The diameter of each near its opening is about 0'03 mm. Each 

 csecum is made up of two rows of cells alternating more or less 

 regularly on the two sides, the narrow lumen taking a zigzag course 

 between them. The individual cells are very large, the long diameter 

 of each being the diameter of the organ itself. The nucleus is large 

 and transparent, but the rest of the cell contains a large quantity of 

 a granular deposit which gives the organs their intense white colour. 

 During pupal life I have noted no important changes in these organs. 



Such is the structure of the alimentary canal and its appendages 

 at the commencement of pupal life— a structure adapted to the life 

 of the larva, but not to that of the imago, and the changes Avhich it 

 undergoes during the pupal period are so great that at the end of 

 that period no part of the whole canal corresponds in structure to 

 the above description. 



The most striking change is the reduction in thickness of the 

 epithelium which occurs throughout, but which is perhaps best 

 shown in the stomach. Four stages of the change are shown in 

 Figs, 3, 4, 5, and 6, which are drawn from the epithelium of the 

 hinder part of the stomach. The beginning of the change has 

 already occurred before the pupa leaves the larval exuvije, but the 

 first stage here shown (Fig. 3) is from a young pupa. At the base 

 of each of the large epithelial cells may be seen one or two nuclei ; 

 a little later the protoplasm of the cell divides into a small portion 

 around the new nuclei, and a much larger portion, which rapidly 

 undergoes degeneration and, separating from the basal laj-er (the 

 new epithelium), is apparently digested. The outer surface of the 

 stomach is covered by an exceedingly thin layer in which I could 

 not make out any structure, but which is presumably muscular, and 

 is at first folded longitudinally (Figs. 4 and 5), but afterwards 

 becomes even, the new cells at the same time becoming flattened 

 (Fig. 6). 



