PHYSIOLOGY OF THE INVERTEBRATA. 265 



Each layer is composed of polygonal nucleated cells. The 

 granules are doubly refractive, contain uric acid, and 

 probably consist of urate of ammonia. Hence the cells of 

 the layer which contain them are termed by Schulze the 

 'urate cells,' while he calls the others the 'parenchyma 

 cells.' The branches of the tracheae which ramify among 

 the parenchyma cells end, like those of other parts of the 

 body, in stellate nucleated corpuscles, one process of the 

 corpuscle passing into a ramification of the trachea. Schulze 

 is inclined to think that the other processes end in paren- 

 chyma cells. The nerves of the photogenic plates are derived 

 from the last albdominal- ganglion ; they branch out between 

 the parenchyma cells into finer and finer branches, which 

 eventually escape observation." (Huxley.) 



Lampyris can vary at will the intensity of the phosphoric 

 light. It has been stated that the light is connected with 

 the action of oxygen upon a fatty material secreted by the 

 photogenic organs, and the light so produced is reflected by 

 means of the granules already alluded to. 



The function of the Malpighian tubules of insects were not 

 definitely established until a few years ago. Some zoologists 

 stated that they represented the " liver," while others main- 

 tained that they were renal in function. 



The Malpighian tubules of Blatta {Periplanetd) have been 

 shown by the author* to contain uric acid and urea. 



Dr. 0. A. MacMunn f has confirmed the author's investiga- 

 tions, for he has extracted uric acid from the Malpighian 

 tubules of Feriplaneta orienialis. These tubules were crushed, 

 boiled with distilled water, the extract evaporated to dryness, 

 washed with hot alcohol, and again dissolved in boiling water 

 and filtered. To the filtrate excess of acetic acid was added, 

 and in some hours uric acid crystals of various forms, and 

 giving the murexide test, were formed. 



* Chemical News, vol. 52, p. 195. 



t Journal of Physioh'jy, vol. 7, p. 128. 



