1917-] C. R. N. Rao : Iridocytes in Batrachian Larvae. 283 



progresses is changed into intense black. The veiitral surface of 

 all these larvae is dead chalky white, more or less speckled on the 

 throat and the sides. On the dorsal surface one meets with every 

 shade of colouration, ranging from bright yellow to dark brown, 

 with or without spots. A few exceptions may be cited to this 

 prevailing scheme of colouration For instance, the perfectly grey 

 larvae of Rh. plitrostictus , which bear numerous round black spots, 

 and are perhaps the biggest tadpoles yet discovered in India. ^ 

 The yellow dorsal streak of the larvae of R. breviceps and R. tigrina 

 is only a premature appearance of an adult character, and the 

 round red spots on the back and thighs of the same tadpoles are 

 mainly larval features. In a few cases like R. alticola and R. liebigii 

 the tail may be- diversified by ocelli or vertical bars. 



The tadpoles of Bufo are all uniformally brown. Occasionally 

 there are metallic dots on the dorsal surface, the ventral side being 

 dirty white as in B.microtynipanum. 



Aitei this brief survey, it need only be mentioned that the 

 outstanding character of the larvae of M. ornata and M. rubra is 

 the possession of metallic bands and surfaces which make the 

 colouration as a whole markedly striking. 



Biological Significance. 



The larvae of M. ornata and M. rubra float on the surface 

 in comparatively large shoals chiefly in the middle of the pond. 

 In the aquarium the same habits are exhibited by these tad- 

 poles. 



Other tadpoles of the Ranid group, which I have reared and 

 kept under observation, are unable to lemain at the surface for 

 any length of time being without the provision of a special struc- 

 ture like a float, as in Megalophrys montana. The ability to remain 

 at the surface throughout metamorphosis is a feature that has some 

 structural bearing. When the animal remains stationary at 

 the top it is really occupying a plane of least effort, which it can 

 do only when the body is for the time being lighter than the water, 

 bulk for bulk. The gill chambers of the larvae of the two species 

 of Microhyla possess large cavities filled with air, which can be 

 easily seen through the transparent skin. These air spaces account 

 for the enormous size of the cephalic region. On pressing the bulg- 

 ing portion of the throat, large bubbles of air may be driven out 

 through the spiracle. An examination of the transverse and longi- 

 tudinal sections of the larvae reveal these air cavities, situated 

 between the first and the second and the second and the third gill 

 arches on each side of the pharynx. This structural peculiarity, 

 absent in the Ranid group (as revealed by sections), which bears 

 some resemblance to the secondary air sacs of Clarias, accounts 



' In my experience the dimensions quoted by Anderson for A", cyatioplilyctis 

 {Proc. Zool. Soc. Loudon, 1895, p. 660) are not of the normal tadpole. If meta- 

 morphosis, however, is hindered throug-h any cause the lar\ae attain such a size. 



