PRESIDENTIAL ADDRESS SECTION D. 85 



organs are also indicated by hyperpituitarism and hypertrophy of 

 the parathyroids apparently resulting from thyroidectomy of 

 amphibian larvae. Pineal secretion seems to react on the chromato- 

 phores or melanophores of the skin, causing them to contract, and 

 so producing striking temporary changes in colouration, which is 

 not without interest when the archaic function of the pineal body 

 as an eye structure is remembered. 



The present author found that fresh extract of sheep's thyroid 

 gland induced rapid division of trypanosomes in vitro, more rapid 

 than the normal. 



Fisheries Work. 



Fisheries development has received considerable attention 

 during the last few years both in Europe and America, while a new 

 beginning has been made recently in South Africa. Such develop- 

 ments have, in many instances, been made possible by purely scien- 

 tific work, undertaken with no idea of immediate economic appli- 

 cation. Thus, the development of the great north-western fishing 

 grounds of Great Britain resulted from the endeavours of Wyville 

 Thomson and others to determine the presence or absence of life 

 in the deep sea. 



Work on the life-history of flat fish, e.g., plaice and soles, has 

 led to transplantation on a large scale off the English coasts, and 

 fish hatching experiments, similarly, have led to the stocking of 

 inland waters in America, resulting in great increase of the avail- 

 able food of the people. A start has also been made in South 

 Africa, and the trout hatcheries have done useful work. 



Commercial use has been made of the scientific investigations 

 of the life-histories of crabs, lobsters and crayfishes, and large 

 canning industries have arisen therefrom. As a result of the In- 

 vestigations mentioned, protection Taws have been enacted with 

 regard to females in berry, the enforcement of the said laws pre- 

 venting the destruction of ova, with subsequent increase in the 

 bulk of Crustacea available for human food. Similarly, scientific 

 work on the life and habits of oysters and mussels permitted of the 

 utilisation of a hitherto neglected source of food supplv. 



Again, the study of larval stages of molluscs has led to the 

 establishment in America of numerous freshwater mussel fisheries, 

 providing nacre for pearl buttons, and of pearl-shell farms in the 

 Red Sea. 



Much attention has been given by zoologists to the subject of 

 the physico-chemical environment of organisms and its influenc° 

 on the observed variations of animal and plant life in the sea. It 

 is known that there are seasonal variations in the marine plankton : 

 but the causes of this periodicity are not. known with certaintv. The 

 warm waters of the tropics are said to support a less abundant 

 plankton than the cold polar waters. Probablv to be correlated 

 with this is the observation that the nitrogen concentration in 

 tropical waters is low, being higher in cold waters. A^ain, the 

 hvdrogen-ion concentration, as tested by the relative degree of 

 alkalinitv or acidity of sea-water, has been investigated in relation 



