178 GRALL^. 



sun, cradled in the luxuriant but soft vegetation which the 

 solar energy produces ; and, therefore, their numbers diminish 

 as one approaches the cold latitudes. In our own country? 

 the total number, and especially the number of species south 

 of the Thames, is greater than north of the Tweed. But 

 the Neuroptera increase vastly towards the north. 



Where there are many winged flies, there must be more 

 larvae, and, generally speaking, the larvse are bred and the 

 winged ones finally deposited in the marshes. The sludgy 

 shallows, which are congealed to a considerable depth in the 

 winter, and are not at any time very fit for swimming in, 

 contain few fish ; and, therefore, the produce of the summer, 

 and a very abundant produce it is, is left to the marsh birds, 

 which resort thither in incredible numbers. In the autumn 

 they find their way southward, and seek their food in various 

 localities, according to mutual adaptation. 



Taken altogether, these birds, throughout both summer 

 and winter, inhabit a zone of considerable breadth, so that 

 some of them only reach the one extremity of Britain in 

 the one season, and some the other extremity in the other ; 

 while certain species, which migrate in other countries to a 

 greater length than that of this island, come in laterally as 

 stragglers ; indeed, as there is no land well adapted for these 

 birds, either directly north or directly south of Britain, the 

 whole of their migrations may be said to be rather oblique, 

 than directly upon a meridian. 



Their migrations are not regulated by exactly the same law, 

 or carried on to the same extent, as those of the warblers. 

 The marsh continues to yield food until it is sealed up by the 

 frost ; but the leaf falls before the ground is frozen, and the 

 caterpillars disappear long before the fall of the leaf. Thus 

 there are species of the marsh birds which do not migrate far 

 in any country, and which with us only change seasonally 

 between the inland marshes and the marshes by the sea, or 



