SECTIONAL TRANSACTIONS.— D. 371 



a certain evaluation obtained of the rdle of cytology in the sphere of systematic 

 classification. 



Prof. E. A. Spaul. — The anterior pituitary and secondary sexual characters 



(II.O). 



Dr. V. B. WiGGLESWORTH. — The rdle of hormones in the grotvth and repro- 

 duction of insects (11.30). 



Experiments on the blood-sucking bug Rliodnius show that moult' ng is 

 brought about by a hormone secreted into the blood. A hormone is also 

 responsible for preventing metamorphosis in the young stages of this 

 insect ; so that by suitable experiments it is possible to produce diminutive 

 adults from first-stage nymphs newly hatched from the egg, or giant nymphs 

 instead of adults from fifth-stage nymphs. The hormone which prevents 

 metamorphosis throughout nymphal life is secreted by the corpus allatum. 

 In the adult another hormone from the corpus allatum is necessary for 

 egg-development in the female and the proper activity of the accessory 

 glands in the male. 



Mr. H. Waring. — Colour change in elasmobranchs (12.0). 



With few exceptions, all Elasmobranchs so far investigated pale (con- 

 tracted melanophores) on an illuminated white background and darken 

 (expanded melanophores) on an illuminated black background. 



It is established that in all these fish, the dark phase results from the 

 secretion of a blood soluble hormone by the neuro-intermediate lobe of the 

 pituitary. In regard to the mechanism underlying the pale phase, however, 

 work on different species has led to divergent opinions. Thus, it has been 

 shown that in certain English species of Raia and Scyllium the pale phase is 

 dependent on the anterior lobe of the pituitary and not on direct nervous 

 control of the melanophores. On the other hand, American workers have 

 concluded that in Musteliis canis paling is brought about by direct nervous 

 control of the melanophores ; but the role (if any) of the anterior lobe of the 

 pituitary has not been investigated. 



The present paper analyses the possibility of different paling mechanisms 

 within the group Elasmobranchii, particularly in the light of some new 

 observations on the dogfish Acanthias. 



Prof. E. Raymond Hall. — Variations in American stoats (12.30). 



Afternoon. 



Dr. R. J. PuMPHREY. — The evolution of hearing (2.15). 



It is customary to make an arbitrary distinction between the senses of 

 ' hearing ' and ' feeling.' This distinction is based on introspection and 

 is due to the peculiar nature of the mammalian ear. In more primitive 

 animals it vanishes and we can distinguish only more and less sensitive 

 receptors for mechanical stimuli. 



The passage of a train of sound waves through a medium is accompanied 

 by two dependent processes, an oscillation of the molecules of the medium 

 about a mean position, the displacement and a rise and fall of pressure about 

 a mean value. Either of these properties may be used to estimate the 

 intensity of the sound, and sense-organs sensitive to sound can be divided 



