igiy-l C. R. N. Rao : Iridocytes in Batrachian Larvae. 291 



the blue of K. variegata nothing can be said about the absorption 

 band of this pigment. 



Synthesis of Iridocytes and Argenteum. 

 The iridocytes are most unstable and are easily affected and a 

 few observations made in the aquarium may be here set forth. 



1. If light should be absolutely cut off from the specimens, 

 the iridocytes are absorbed in about 4 or 5 days but not the argen- 

 teum. 



2. Starvation produces the same effect, and the time (4 or 5 

 days) depends on the condition of the larva previous to the com- 

 mencement of the experiment, 



3. Exposure to sunlight and liberal feeding produce two 

 effects. The larvae become absolutely transparent, head and body 

 included, and the metallic dorsal band extends over the cranium, 

 at the same time becoming most brilliant. 



4. If specimens used in experiments (i) and (2) are restored 

 to normal conditions, the water (preferably tank water being used) 

 in the aquarium being renewed everyday, nearly 70 per cent of them 

 acquire the dorsal band, appearing first in the anterior region of 

 the vertebral column. 



Summary. 



The leading facts discussed in this paper may be now sum- 

 in arised. 



The first set of facts relate to the floating habits of the larvae 

 of M. ornata and M . rubra co-related with the presence of air-cham- 

 bers between the branchial plates, which function more or less as 

 hydrostatic organs. The danger of exposure to the attacks of 

 enemies incidental to such habits is warded off by the presence of 

 an acid offensive matter in the cephalic gland. This circumstance 

 is probably advertised by the bright colouration. 



The second set of facts deal with the unique occurrence of 

 iridocytes and argenteum in the same larvae. Both from the mor- 

 phological and evolutionary points of view the presence of irido- 

 cytes and black chromatophores on the lungs and peritoneum is 

 full of significance, for their occurrence in the air-bladder of fishes 

 and the peritoneum of embryonic fishes has been reported. It is 

 established that the iridocytes of the mid-dorsal band, and the 

 ventral argenteum of the subcutaneous tissue on the sides and the 

 ventral surface of the abdomen of these tadpoles, are entireh^ free 

 from calcium in any form, and, while both are in some respects 

 identical with those of fishes, are entirely different from the Gua- 

 ninkalk of Ewald and Kriikenberg. The substance composing 

 the iridocytes occurs in the form of irregular plates consisting of 

 spherical granules, identical with those obtained by the breaking 

 down of the guanin nitrate crystals, while the argenteum is a 

 dense opaque reflecting subcutaneous tissue in which no structure 

 can be made out. The dead chalky white on the ventral surface 

 of the larvae of the genus Rana is due to guaninkalk. 



