182 Psyche [December 



At times the epithelium also appears transversely striated, i. e., 

 at right angles to the length of the tube; especially in sections 

 or when teased fresh in potash. When the malpighian tubes 

 are swollen with urates, etc., if placed in weak acetic acid the entire 

 contents — urates, intima and epithelium — are quickly evacuated, 

 and the basement and peritoneal-membranes left as an empty shell. 



The cells of the epithelium of the tubes seem to disintegrate 

 locally and be replaced by new cells, and frequently (when fully 

 loaded and distended with urates, etc.) the epithelium of long 

 portions of the tubes appears to disintegrate and to fall into the 

 lumen, dissolve and be discharged into the rectum, new cells 

 taking their place. This seems to recur several times during the 

 life of the insect. At all times some of the cells can be seen in 

 sections secreting large globules of matter into the lumen. The 

 distal ends stain much more heavily than the rest of the tube. 



The contents of the malpighian tubes give a decided reaction 

 to the murexide test; when the tubes are white and swollen they 

 contain a very large quantity of urates of soda and ammonia 

 in minute roundish granules, appearing to the unaided eye as a 

 whitish sediment; under the microscope they appear white by 

 reflected and pale yellow-brown by transmitted light. By treat- 

 ment with dilute acetic acid (2 per cent.) very many large color- 

 less crystals and bundles of crystals of uric acid 1 are usually to 

 be seen, which resist the action of hydrochloric acid. Calcium 

 oxalate crystals also occur in numbers, and do not dissolve in 

 water nor in acetic acid, but are entirely dissolved by hydrochloric 

 acid. They may be distinguished microscopically by their form 

 (squarish, with two diagonal lines from corner to corner), and 

 chemically by the decoloring of permanganate of potash added 

 to a solution of the calcium oxalate crystals in sulphuric or hypo- 

 chloric acid. 



Sometimes, on leaving the tubes in water for about twenty- 

 four hours, they are surrounded by a layer of mucilaginous matter 

 which appears to have exuded from the whole of the tubes except 

 the distal ends. Occasionally the tubes are very irregularly 

 swollen here and there into lumps, and are then usually of a bluish 

 hyaline appearance. In this state, which is not common, they 



1 And also what look very like hippurie acid crystals. 



