86 PRESIDENTIAL ADDRESS SECTION D. 



to marine life. Alkalinity has been found to be low in summer, 

 to increase somewhat in autumn, to disappear in winter, and to 

 reappear again in spring (March) at Port Erin, Isle of Man, reach- 

 ing a maximum in April or May. This change corresponds roughly 

 to the change in the phyto-plankton observed there. It has been 

 shown also that the diatoms increase in numbers when the water 

 is at its coldest, and these are followed by swarms of Copepods. 

 The number of Copepods in a given area determines the presence 

 or absence of swarms of fish, such as herring and mackerel, that, 

 prey on them. As Crustacea feed largely on diatoms and flagel- 

 lates, a knowledge of the distribution of these may be sufficient 

 to initiate new enterprises in fishery work. 



It is well known that the great intermediate zone of waters 

 between surface and bottom used to be considered lifeless. 

 Thomson's work, to which reference was made earlier, showed that 

 this was not the case. Recently, according to arguments advanced 

 by A. H. Church, such a zone of waters has a special evolutionary 

 interest, since it was possibly from a former world-wide ocean of 

 ionised water that the first living organisms were evolved to become 

 later the floating unicellular plants of the primitive plankton. 



Cytology and Sex. 



An enormous amount of work has been done on cytology 

 during the last twenty years. Among the pioneers mention may 

 be made of Boveri and E. B. Wilson. It is quite impossible even 

 to attempt to outline this work. Perhaps notice of some recent 

 work may suffice before we pass on to consider work on chromosomes 

 and sex. 



Outside the nucleus of the cell and within the cytoplasm are 

 the Golgi apparatus and mitochrondria. Within the nucleus in 

 addition to chromosomes are nucleoli. The nucleoli are either 

 plasmosomes or karyosomes. The independence of the nucleolus 

 and the chromosomes has been shown in the division of the cell. 

 The nucleolus is an important element in the cell, being concerned 

 with important metabolic functions. Gatenby considers the 

 nucleolus to represent trophochromatin and the chromosomes to 

 represent the gonochromatin. 



Most interesting and promising advances have arisen from 

 studies of the chromosomes of the germ cells of certain animals, 

 especially in connection with Mendelian experiments with hybrids. 

 The chromosomes are stainable bodies in the nucleus of a cell, 

 especially of a germ cell, that carry hereditary characteristics, both 

 physical and mental, from the parent to the children. Formerly 

 it was thought that the chromosomes of the germ cells of the two 

 sexes were the same in number. However, an accessory chromo- 

 some was discovered by several observers, who found that in the 

 males of certain insects belonging to the Hemiptera and Ortho- 

 ptera there was one chromosome that behaved differently from its 

 fellows during maturation or reducing divisions. This chromosome 

 took no part in the pairing of the maternal and paternal chromo- 

 somes, but passed undivided to one pole of the division spindle. 



