PUZZLES AND PARADOXES 263 



to attain this end with the least possible expenditure of 

 energy is to rear up the hinder end of the body and to 

 squeeze out therefrom a sticky juice, akin to that of the 

 silk-forming caterpillars. This juice exudes from four 

 separate apertures, and forms, on exposure to the air, as 

 many threads. These are soon caught by the breeze, and 

 speedily, delicate life-lines of several yards in length are 

 being wafted about. At last so much has been paid out, 

 that the body of the tiny spinner is lifted up from the 

 ground and borne aloft, to be transported, perhaps, for 

 miles. When the breeze drops the little aeronauts descend, 

 and finding congenial country, settle down to grow into big 

 spiders, and wander no more. 



It is obviously of vital importance to species which in 

 their adult state are almost or quite sedentary, that some 

 means of emigration should be devised for the young : 

 it is of importance to the individual since it averts famine, 

 and of importance to the species since thereby it escapes 

 extermination. 



Dr. Watts long since assured us that " birds in their little 

 nests agree," and this is, as a rule, perfectly true : indeed, 

 cases are on record where the young of the first brood 

 assist their parents in feeding those of the second. The 

 waterhen affords a case in point. 



But a ferocious contrast to this picture is the case of 

 nestling buzzards. With the buzzards, as with all the 

 birds of prey, the eggs are incubated as soon as laid. As 

 a consequence the bird first hatched is several days older 

 than the youngest. Being thus stronger and hungrier 

 than its nest-fellows, it contrives to get the lion's share of 

 the provender. Now, when the nursery is built among 

 the hills, where food is relatively scarce, there are often 

 long breaks between meals, and not seldom, during one of 



