40 Psyche [April 



only two cells, both so much swollen as to reduce the lumen to 

 a mere line, except at one side where the wall is reduced to a mere 

 membrane bounding a small passage. The canal may be even 

 more reduced than in the section figured, but it is commonly slit- 

 like and was never seen to be large and circular in this region. 

 The cells are vacuolated and contain some darkly staining granules. 

 A section through the intermediate narrow portion of the tubule 

 just in front of the photogenetic region and corresponding with 

 the point S in Fig. 2 is shown in the upper drawing of Fig. 4. 

 The lumen, though similar to that in the anterior region, is more 

 evident. The cell content is denser and more granular and 

 approaches that of the cells in the luminous organ. All four 

 tubules of this latter region are shown in cross-section in Fig. 7. 

 They are circular, with large lumina, and the walls consist of four 

 well-defined cells, with large spherical nuclei. Their cytoplasm 

 is throughout densely packed with minute granules which stain 

 very deeply, so that the tubules stand out in marked contrast 

 with the underlying reflecting layer. Evidently these granules 

 correspond in function with the photogenetic granules in the 

 luminous organ of the fire-fly. Vacuoles are rare or altogether 

 lacking in these cells, as in the section figured. The lumina of 

 the tubules, often enclose a granular deposit which may represent 

 the stained residue of a liquid contained in them during life. 

 The extreme tips of the Malpighian tubules, shown in section in 

 Fig. 6, recall the structure of the anterior excretory portion, 

 since the large granular cell-wall here thins out dorsally to a deli- 

 cate membrane which closes the end of each of the tubules. 



Although the luminous organ of the pupal and imaginal Bolito- 

 phila has not been studied we may safely assume that it is the 

 same as that of the larva. This is clearly indicated by Hudson's 

 statement that in both the larval and pupal instars it is the last 

 abdominal segment which is luminous, and the fact that at least 

 in Nematoceran Diptera, if we accept the studies of Vaney (1902) 

 on Siniulium and Chironomus, the larval Malpighian tubules are 

 not broken down during metamorphosis but persist with their 

 structure essentially unaltered in the pupa and imago. 



The conversion of the distal portion of each of the four Mal- 

 pighian tubules into a luminous organ in Bolitophila is of consider- 

 able interest both morphologically and physiologically; morpho- 



