PRESIDENTIAL ADDKESS. 717 



America, where large organisations are devoted to the combat with the iusect 

 enemies of agriculture. We are fortunately spared some of the worst of the foes 

 of vegetation which devastate other lands. But many of our cultivated plants 

 suffer severely from the ravages of insects and arachnids ; and it is perhaps not 

 too much to hope that more systematic measures will some day be taken in 

 this country to disseminate the knowledge by which this injury to agriculture may 

 be minimised. 



As a last illustration of the way in which Zoology comics into relation with 

 practical matters, I may allude to the question of fishery investigation. Although 

 much remains to be done in this connection, the importance of purely scientific 

 work has been to some extent officially recognised. The Board of Agriculture 

 and Fisheries in England, the Scottish Fishery Board, the Fisheries Branch of 

 the Department of Agriculture and Technical Instruction for Ireland, and other 

 organisations which are mainly or entirely supported by private funds, are in part 

 devoted to the interests of the fishing industry. The Government have latterly 

 participated in an international investigation of the North Sea, as the result of 

 which many interesting facts have been recorded with regard to the life-histories 

 of food-fishes, their migrations at various periods of life, the age at which they 

 become sexually mature, and the nature of their food. These are questions that 

 demand study by experienced Zoologists ; and the interrelations of food-fishes and 

 the organisms on which they subsist or with which they come into competition are 

 so complex that a full study of the entire marine fauna appears to be a necessary 

 preliminary to the elucidation of the questions of immediate practical utility. 



I have tried to indicate that Zoology is a subject that has important relations 

 with the practical concerns of mankind. But in Zoology, as iu other branches 

 of science, the principal advances have been made by investigators who have 

 studied it for its own sake, without thought of the practical outcome. It would 

 undoubtedly be a misfortune should an entirely utilitarian spirit become dominant 

 in the pursuit of science. In the full conviction of the truth of this statement I 

 venture to invite your attention to certain questions connected with the Polyzoa — a 

 somewhat neglected group of animals which I do not profess to be able to connect 

 in any direct way with practical matters. In choosing this subject I have been 

 influenced by the belief that it is well for the President of a Section to speak on 

 matters of which he has had practical experience. 



During the course of my studies on the Polyzoa I have been conscious of the 

 existence of many unsolved problems and difficulties, some of which are con- 

 nected with the functions, distribution, and variations of certain remarkable 

 appendages known as ' aviculai'ia ' and ' vibracula.' Although the facts bearing 

 on the significance of these organs are familiar to specialists only, they appear to 

 me capable of throwing light on questions of general Biological interest, particu- 

 larly in connection with variation in animals that increase by budding. 



The statement has often been made, as the result of a theoretical conception of 

 the physical basis of heredity, that the asexual method of reproduction gives rise to 

 little or no variability. Although there are many reasons for doubting the validity 

 of this conclusion, it may be well to state at the outset that the Polyzoa, which 

 are without exception characterised by increasing in an asexual manner, show a 

 high degree of variability in the individuals thus produced. So much is this the 

 case that the want of fixity of type which results from the tendency to vary 

 renders the definition of species particularly diflicult in this group of animals. 



Meeting as we do at Dublin there is a special appropriateness in discussing 

 the Polyzoa, as a tribute to the memory of a distinguished Irish naturalist, J. V. 

 Thompson, to whom we owe not only the name Polyzoa, but also the first clear 

 conception of what these animals really are. In the fifth memoir, published at 

 Cork in 1830, of a short but brilliant series of papers,' Thompson was the first to 

 demonstrate the essential nature of the differences between the Polyzoa and the 

 other ' Zoophytes ' with which they had previously been classified. G. J. Allman, 

 wLo at a later period did so much to throw light on the structure and natural 



^ ^Zoologwal Besearches and Illustrations. 



