330 SECTIONAL TRANSACTIONS.— D. 



disease of the teeth, &c., showing that they must have been living in life-optimum 

 conditions. In the uppermost layers there is a series of pigmy forms leading to 

 extinction. 



This example clearly demonstrates that the attainment of a Ufe-optimum, after 

 a more or less hard struggle for existence, is the greatest danger for a species' further 

 evolution. It cannot be an isolated case, and probably those of the Dinosaurs, 

 Ichthyosaurs and Plesiosaurs are other examples. A Ufe-optimum will never produce 

 any further evolution but only degeneration and, in consequence, extinction. 



Prof. J. Graham Kerr, F.R.S. — Spirula and the Morphology of the 

 Siphonopoda. 



Mr. J. T. Cunningham. — The Vascular Filaments on the Pelvic Limbs of 

 Lepidosiren, their Function and Evolutionary Significance. 



In a publication on Fishes in 1912 Mr. Cunningham suggested that the water in 

 the nest-burrow of Lepidosiren was probably deficient in oxygen, and that the function 

 of the filaments on the pelvic limbs of the male when guarding the eggs was to provide 

 oxygen not for itself but for the eggs and young, in other words not to absorb oxygen 

 but to give out oxygen. Dr. G. S. Carter and Mr. L. C. Beadle in their recent expedition 

 to the Paraguayan Chaco experimentally established the fact that the water of the 

 swamps in which Lepidosiren lives is almost entirely de-oxygenated except at the actual 

 surface, and independently drew the same conclusion that the pelvic filaments of the 

 breeding male have the function of giving o£E oxygen for the respiration of the eggs and 

 larvae. 



As it has not yet been possible to make experiments on the male Lepidosiren with 

 regard to this point, Mr. Cunningham has made numerous experiments to ascertain 

 whether the ordinary respiratory organs give oS oxygen when fish or amphibia are 

 placed in de-oxygenated water. The general result of these experiments is to show 

 that oxygen is undoubtedly emitted, but it is difficult to distinguish what comes from 

 the giUs and what from the skin or other parts. 



Assuming that reversal of oxygen-absorption takes place in the filaments, the case 

 appears to be unique in the animal kingdom, though of course excretion of oxygen is 

 known in the air-bladder of fishes. It is maintained that such a special adaptation 

 cannot be rationally explained on the hypothesis of mutation undetermined by condi- 

 tions. On the other hand, the question arises what kind of stimulus could give rise to 

 such filaments in the individual. It is suggested that the pelvic limbs may have been 

 used originally to move the eggs and larvEe about, and that not only the friction but 

 the absorption of oxygen from the limbs may have been a stimulus to the growth of 

 the vascular filaments. A similar stimulus may have acted in the case of the various 

 larval respiratory organs in Amphibia, and in that of the allantois which is the embrj;^- 

 onic respiratory organ in Birds, Reptiles, and Mammals. This is believed to be the 

 first time that it has been suggested that the passage of oxygen through the tissues 

 may act as a special stimulus to the growth of tissues and blood vessels, although it is 

 in accordance with the general principle that functional activity causes growth which 

 results in better adaptation to the function. 



Miss A. E. Miller. — The Vertebral Column of Lepidosiren paradoxa. 



Mr. F. W. FiTzSiMONS. — Snake Venoms, their Uses and Possibilities. 



Afternoon. 



Demonstration Session (Sections D, I), in Prof. L. T. Hogben's 

 Experimental Laboratory. 



Mr. C. Gordon. — The Permeability of Animal Tissues. 



Prof. L. T. HoGBEN. — Conditioned Phenomena in Xenopus. 



Enid Hogben. — The Respiratory Exchange in the Freshwater Crab. 



