PBBKUARY 49 



also at stations all along the eastern coast of Britain, 

 and these birds would not go near Heligoland. Though 

 greatly diminished in numbers, the northward migration 

 in spring is equally well marked. 



'Imagine (says Herr Gatke) a mild and clear evening in 

 Spring, the sun has set long since . . . the last soft note of 

 the redbreast has died away, and for a considerable time no 

 sound has disturbed the scented stillness of the air. Suddenly, 

 through the silence, the clear, fine note of our little wren is 

 heard ; and soon afterwards the bird is seen rising from the 

 neighbouring bushes against the luminous evening sky. At 

 measured intervals its call-note "hiit, hiit, hiit" is heard as it 

 flies off in slightly ascending spirals over the neighbouring 

 gardens; then from every bush — here, there, near and far — 

 the cry is answered, and from all sides his travelling companions 

 mount upwards in the wake of the earliest starter. Assured 

 by the answering voices that all the sleepers are aroused, he 

 ceases circling about, and rises almost vertically with brief and 

 rapid strokes. Soon all assemble in a somewhat loose swarm ; 

 the call-notes are silenced when the .last straggler has joined 

 the departing flock, and the tiny wanderers vanish from sight.' 



VI 



Few subjects provide more perplexing conundrums to 

 the reflective loafer in the country than the The ProWem 

 distribution of certain fresh- water fishes on the of Dispersal, 

 surface of the globe. Having regard to the variability of 

 most families of fish, which is far greater than that of 

 other and higher vertebrates, and to the striking changes 

 wrought in the appearance of species, and even of 

 individuals, by differing conditions of climate, soil, food, 

 and general physical environment, it is startling to find 

 that, although in countless instances these agencies have 



D 



