284 Records of the Indian Museum. [Vol. XIII, 



for the floating habit of the tadpole and like the fish it blows out 

 a few bubbles of air through the mouth or the spiracle before sink- 

 ing to the bottom. 



While floating, the tadpole must be peculiarly exposed to at- 

 tacks from enemies who may have some difficulty in hunting for 

 other forms which lead a concealed mode of life. It is obvious 

 that unless there is some special provision which to a greater or 

 less extent secures immunity, the larvae of Microhyla will utterly 

 perish. 



Observation shows that in the aquarium these larvae are avoid- 

 ed by both fish and snakes, hke Clarias, Saccobranchus, Ophio- 

 cephalons and Tropidonotus, and in ponds ducks and geese also do 

 not touch them. They, however, greedily seize and devour other 

 amphibian larvae. Reference has already been made to the oc- 

 currence of a cephalic gland and it is clear that the offensive 

 matter, by which the larvae are protected, is situated in this gland. 

 When a scraping from this gland was introduced into the conjunc- 

 tiva of a dog, the eye was kept closed and at the same time it 

 became blood-shot with a watery discharge. If an entire larva 

 be placed in the mouth, nothing will induce the dog to swallow 

 it ; those of Rana are, however, swallowed. The fish Opiocepha- 

 lus was tried. Forcible feeding of the fish was found to be futile, 

 for as often as the larvae were introduced into the mouth, they 

 were thrown out with considerable force. The secretion is acid in 

 reaction, as may be tested with blue litmus paper. The coloura- 

 tion may have a warning efliect. 



The Colour Elements. 



For convenience of treatment, the colour elements of the 

 larvae of M. ornata may be considered under the following heads : — 



1. Black chromatophores of the melanin group. 



2. Coloured pigments of the Hpochrome group. 



3. Iridocytes which are guanin crystals, occurring chiefly in 



the form of plates. 



4. Argenteum or reflecting tissue, on the sides and the ventral 



regions of the abdomen. 



The first two elements combine in various proportions or in- 

 dividually produce the several colours referred to already in the 

 foregoing paragraphs, while the latter elements account for the 

 metallic brilliance The dead chalky white on the ventral surface 

 of Ranid larvae is due to the argenteum being impregnated more 

 or less with calcium, the compound thus produced being known 

 as guaninkalk. 



I. Black Chromatophores. 



These elements occur in chiefly two forms, as mere dots and 

 as dendritic structures. The former are confined to regions that 

 are more qr less transparent, such as the head and the caudal 



