PUESIDEXTIAL ADDRESS SECTION D. 65 



must be the goal; applications of knowledge will come later. The 

 investigator is the one to whom the credit is due, not the one 

 who merely sees in knowledge a means to the end for the produc- 

 tion of wealth. 



Pure science extends in many directions, and I think that 

 in the domain of biology the directions are as numerous as in any 

 field of work. Even where the attention of the worker may be 

 theoretically confined to so-called " practical " investigations, it 

 is possible, and ought to be essential, to maintain the standard 

 of those less trammelled. Perhaps in no branch of biology is that 

 m^ore necessary than in the branch with which I am most associ- 

 ated, namely, parasitology. The subject is vast; there are many 

 items of great interest therein ; the litei'ature is often not only 

 scattered, but in journals difficult of access to many scientists, 

 and these are some of the reasons for my choosing as a topic some 

 recent advances in parasitology, perhaps with emphasis on the 

 side of human parasitology, and necessarily with a wide element 

 of selection in the subject matter. Consequently, certain aspects 

 of parasitology as affecting plant life, human and other aniniiil 

 life and our general scheme of society will be touched upon. 



The origin of parasites is undoubtedly from free-living forms. 

 Scarcity of food and other unfavourable environmental conditions 

 probably first caused the habit of living at the expense of some 

 other organism, probably at first a dead organism. From sapro- 

 phytism to parasitism many intermediate stages occur, and it is 

 doubtful where one begins and the other ends. In certain groups 

 of organisms such as the Cestoda, that are exclusively parasitic, 

 links between allied free-living and parasitic forms are less obvious 

 than in the case of such organisms as the Flagellata or the 

 Nematoda, where free-living and saprozoic forms grade almost 

 imperceptibly into one another, and thence on to parasitism. 

 Here it is that morphology and embryology come into promi- 

 nence, for it is by their study that the present forms can be 

 linked with those of the ancestral stock. A sound knowledge 

 of morphology is essential to the parasitologist, as indeed it is to 

 any M'orker in any field of biology. To the parasitologist tlie 

 minute anatomy, the life-histories and the habits of the hosts of 

 the parasites studied are of paramount importance — a fact often 

 overlooked by workers in other domains of biology, such as sys- 

 temic or palseontological work, to mention only two fields. 

 Attention to the value of morphology was recently emphasised by 

 F. A. Bather, in a review of a book on the ancestry of the 

 EchinodeiTns, and his remarks apply equally to the parasitologist, 

 who should be a trained morphologist, and who, unless so trained, 

 can and does draw unwarranted conclusions. Bather wrote : 

 " Whoever discusses morphological problems should have regard 

 to the recognised principles and methods of morphology. He 

 should have a sufficiently wide knowledge of comparative anatomy 

 to be able to estimate the relative values of the facts that he 

 adduces. There is at the present time a real danger that this 

 discipline may be forgotten in the rush after alluring discoveries 

 in genetics, biochemistry and other novel branches of biologj-." 



