NATURAL HISTORY OF SELBORNE. 103 



LETTER XL. 



TO THE SAME. 



SELBORNE, Sept. znd, 1774. 



DEAR SIR, Before your letter arrived, and of my own accord, 

 I had been remarking and comparing the tails of the male and 

 female swallow, and this ere any young broods appeared ; so that 

 there was no danger of confounding the dams with their pulli : 

 and besides, as they were then always in pairs, and busied in the 

 employ of nidification, there could be no room for mistaking the 

 sexes, nor the individuals of different chimneys the one for the 

 other. From all my observations, it constantly appeared that each 

 sex has the long feathers in its tail that give it that forked shape ; 

 with this difference, that they are longer in the tail of the male 

 than in that of the female. 



Nightingales, when their young first come abroad, and are 

 helpless, make a plaintive and a jarring noise ; and also a snapping 

 or cracking, pursuing people along the hedges as they walk : these 

 last sounds seem intended for menace and defiance. 



The grasshopper-lark chirps all night in the height of summer.* 



Swans turn white the second year, and breed the third. 



Weasels prey on moles, as appears by their being sometimes 

 caught in mole-traps. 



Sparrow-hawks sometimes breed in old crows' nests, and the 

 kestril in churches and ruins. f 



There are supposed to be two sorts of eels in the island of Ely. 

 The threads sometimes discovered in eels are perhaps their young : 

 the generation of eels is very dark and mysterious.} 



Hen-harriers breed on the ground, and seem never to settle on 

 trees. 



* Salicaria locuslella, see Letter XVI. 



t We have known a kestril breed in the deserted nest of a magpie. 



I Three species of British eels have now been clearly made out. Two very distinct by 

 the form of the head, in the one narrow, in the. other broad, and consequently have been 

 named sharp and broad-nosed eels. The third is of intermediate form, and called the 

 snig. Ely was famous for its eels, and is said to have derived its name from the circum- 

 stance of its rents being formerly paid in eels. The "threads" would be intestinal 

 worms, perhaps Filarice,-~^,^\& are oviparous and generate like most other fishes, having 

 bony skeletons. 



