I06 FLEAS, FLUKES AND CUCKOOS 



mammals into families and genera, whereas the exoskeleton or hard outer- 

 covering, is used in the case of fleas. 



It is not easy to describe the simplest object in precise language. 

 The layman complains bitterly about the obscure wording of legal 

 documents, emergency regulations and scientific papers. Yet anyone 

 who has tried his hand at describing a piece of Hnoleum or a gate- 

 legged table in such a way that it cannot be mistaken for any other type 

 of floor covering or table, will appreciate some of the difficulties in- 

 volved. A trained lawyer is required to draw up a legal document 

 and a trained biologist to classify an insect correctly and ade- 

 quately. 



Although unavoidable, the use of this technical jargon is, at first, 

 rather irritating and confusing to those who are unfamihar with 

 scientific descriptions. This fact, and also the obscure nature of some of 

 the characters used in separating one species from another, makes 

 systematics and classification seem fantastically dull to the average lay- 

 man. Sooner or later even the professional zoologist reflects gloomily 

 that all roads lead to the counting tray or to the measurement of combs 

 and beaks. Nevertheless this detailed and rather tedious work is 

 absolutely essential. Commenting upon the fact that the spread of 

 epizootic plague is governed by the flea-species factor Hirst remarked : 

 " The discovery is but further testimony to the essential unity of science 

 in its bearings on the welfare of the human race, for it is the natural 

 outcome of the purely zoological researches of Rothschild and Jordan 

 on the systematics of the Siphonaptera." In fact sound systematics are 

 the foundations upon which all biological theories, great or small, are 

 built. Disgruntled zoologists should reflect that Darwin's first important 

 pubhcation was a treatise on the systematics of barnacles. 



Fleas are insects, and share with all other insects certain character- 

 istics of their Class. Within this huge assembly they form a rather 

 isolated Order. They are descended from winged ancestors — a fact 

 which can be inferred from their structure and the study of analogous 

 cases — but the various intermediate types have become extinct and 

 there are no living insects which show the transitional stages or even 

 suggest what they were like. 



When the fleas themselves are divided up they fall into two fairly 

 well defined superfamiUes, and here again we can do Httle more than 

 guess at the characters shared by the common ancestors of these two 

 large groups. The superfamiUes, famihes, genera and species,which 



