290 Records of the Indian Museum. [Vor,. XIII, 



brightness of the mid-dorsal streak is caused by a layer of yellow 

 lipochrome superimposed over the crystals. On the removal of the 

 colouring matter by alcohol or glycerine, the band is transformed 

 into a silver brilliancy. The following crystals were obtained and 

 examined : 



1. Strong solution of iridocytes and argenteum of the tadpole 

 in hydrochloric acid, on being boiled, is precipitated in the form 

 of delicate pointed needles, which on standing unite to form irregu- 

 lar plates. These are not hygroscopic (fig. 3). 



2. Nitric acid solution gives broad plate-like crystals, some- 

 what prismatic, truncated at both ends. They arrange themselves 

 in pectinate groups while hot, and break into spherical granules 

 on cooling (fig. 4). 



3. Sulphuric acid solution, which chars on boiling, produce 

 blunt delicate needles that are bent in parallel rows. They straighten 

 on cooling (fig. 2). 



4. In caustic soda iridocytes crystallise in the form of pyra- 

 midal needles, often aggregated in wisps. The crystals are hygro- 

 scopic (fig. i). 



5. Hydrochloric solution of argenteum treated with MGCL.^ 

 and precipitated gives three forms of crystals : — (i) Long silky 

 fibres ; long spindle-shaped pointed or blunt needles (aggregations of 

 the first) ; (2) small delicate needles arranged in the form of brushes, 

 and (3) smaller needles either isolated or forming rounded plates. 

 The crystals are not hygroscopic (fig. 5). 



6. If ZNCL.^ should be substituted for MGCL,^ in the above, 

 the crystalline forms are rounded with jagged edges. They decom- 

 pose into very delicate yellow needles (fig. 6). 



7. Hydrochloric acid solution of iridocytes treated with 

 strong picric acid will yield tall cylindrical coloured crystals trun- 

 cated at both ends. They are hygroscopic (fig. 7). 



8. If nitric acid solution is used instead of hydrochloric acid 

 in the above, radiating coloured plates more or less oblong are ob- 

 tained. Thc}^ are also hygroscopic (fig. 8). 



9. The silver derivative of oxyguanin also crystallises in the 

 form of short delicate needles. They arrange themselves like 

 wheels with a number of spoke-like structures radiating from the 

 centre and very minute concentric circles. Between any two of 

 such aggregations the silver oxide, which is also formed, is deposited. 

 The crystals are hygroscopic and unstable (fig. 9). 



There is only one primary form of crystals of iridocytes 

 and argenteum obtained from all these sources which, under 

 the influence of different substances, assumes widely divergent 

 shapes. 



The lipochromes are easily soluble in alcohol and solutions of 

 yellow and red pigments were employed for wave length measure- 

 ments of the absorption band with negative results. It is possible 

 that the red in the tail of the forms mentioned above and other 

 larvae is only a concentrated form of the yellow pigment. As a 

 solution of any degree of concentration could not be obtained of 



