MARINE BIOLOGICAL STATION AT PORT ERIN. 43 



investigation is, of course, beset with difficulties, but they 

 are not insuperable. One great difficulty is to determine 

 to what extent we can safely draw conclusions from our 

 observations. 



It may help to realise the problem if I take 

 a homely illustration and liken the investigation to 

 the case of an aeronaut in a balloon trawling along the 

 streets of Liverpool through a thick fog. We may 

 suppose that a drag in the neighbourhood of University 

 College would yield some students — male and female — 

 and a professor ; one somewhere about the docks would 

 doubtless capture some sailors, dock labourers, and a 

 stevedore or two, while a lucky shot opposite the Town 

 Hall might bring up a policeman, an electric car, and a 

 couple of Aldermen. Now, if such experiences were 

 repeated over and over again, would the con- 

 clusions that might naturally be drawn by the 

 intelligent aeronaut as to the relations between 

 organisms and environment in Liverpool be correct ? The 

 observed association of students with a professor, and of 

 both with a college, would be justifiable. It would be 

 correct to conclude that sailors, dock labourers and steve- 

 dores frequent the docks, and that Aldermen have some 

 connection with a Town Hall; but the fact that electric 

 cars are also abundant in front of the Town Hall is non- 

 essential, and any conclusion such as that Aldermen and 

 electric cars are usually associated with the same habitat, 

 and are in any way inter-dependent, would be erroneous. 



We can imagine many other cases of this kind where 

 appearances might at first be deceptive, and false 

 inferences might be drawn from observed facts. On the 

 other hand, some true conclusions would be clearly indi- 

 cated ; and I do not doubt that it is much the same in 

 our investigations as to the condition and population of 



