340 SECTIONAL TRANSACTIONS.— D. 



well developed chalksacs have this in common, that they jump well, coming down in a 

 normal position, enabling them to make quick successive jumps as a mode of rapid- 

 progress. So the typical Rana's, some Cystynathids, and the Engystomatid 

 Rhinoderma. 



It is very rare that chalksacs are present in a form that is not known to jump well. 

 So Ceratophrys, a toad-Uke Cystignathid, but it may be a good jumper after all. 

 Nototrema, a tree-frog with well- developed chalksacs, seems an exception to the given 

 correlation ; but its hind legs are stronger and not so lengthened for climbing on 

 trees as in typical Hyhds and it may be a good jumper when moving on the ground. 



The observation that well-developed chalksacs on the spinal gangUa are correlated 

 with special jumping power, points to the conclusion that they are connected with 

 the equilibrium in jumping, giving the animal a warning, when it is losing its 

 equiUbrium, perhaps automatically inducing such movements of the muscles of trunk 

 and legs, that equihbrium is regained, working in a quicker way than the ear- 

 labyrinth. 



The chalksacs could then only work by the weight of the otoconia influencing in 

 some way the spinal gangUa. This would explain why the chalksacs are so closely 

 connected with these gangha, including the hindermost of the sacral plexus. It is 

 obvious that in those Anura that jump very far, a special demand is made on the 

 sense of equilibrium. 



The enlarged Saccus endolymphaticus, fiUed with otoconia lying dorsal to the 

 spinal cord, must also be connected with some special need of Anura, as no other 

 Vertebrate possesses the Uke. It is absent in some Anura, that have given up 

 jumping (Aglossa, Discoglossus, Pelobates, Phyllomedusa). Now the only really 

 aberrant character of a primitive Anura was development of jumping power. This 

 could have caused the formation of an accessory static mechanism by enlargement of 

 the Saccus endolymphaticus, but I can only suggest this. 



What I have brought forward is a working hypothesis only for the physiologist. 

 But it may show a way for setthng the function of the Saccus endolymphaticus and 

 of the chalksacs. This communication is made also on behalf of Dr. Pilz, who had a 

 large share in the work reported on. 



Mr. J. H. Power. — Recent Advances in our Knowledge of South African 

 Amphibia. 



The number of described species and sub-species has been considerably added to 

 since the last visit of the British Association for the Advancement of Science. 



Research work in the field has been prosecuted much more systematically, with 

 gratifying results. 



A feature of outstanding interest is that a number of species seem to be confined 

 to the Cape Peninsula. A varied frog fauna numerous in species flourishes along the 

 Indian Ocean coast belt, whereas the Western or Atlantic coast belt, because of the 

 prevailing desert conditions, has only a few species. 



The highly specialised larvae of certain South African genera and species are 

 described, and remarkable instances given where the study of the larvae has thrown 

 light on the affinities of certain South African genera with Asiatic, Australian and 

 American forms. On the whole, the information gained regarding the larvae of the 

 South African Amphibia tends to support the thesis that all forms of a natural group 

 will tend to exhibit the same larval specialisations. 



Friday, August 2. 



Dr. G. S. Carter. — Bionomics of Swamps and Marshes, especially those 

 of the Tropics. 



Miss P. M. Jenkin. — A Preliminary Survey of Certain Tropical Lakes in 

 Kenya. 



I reached Kenya on April 12, 1929, and stayed a night in Mombasa to clear my 

 apparatus through the Customs and to send it up-country on the next day's passenger 

 train. I reached Nairobi on April 14 and purchased a second-hand car ; this was 

 essential to the expedition as my bases were to be at least ten miles from the lakes, and 

 it carried me some 2,000 miles before being sold again on my departure. 



