SECT. X.] INTRODUCTION. 55 



That they may the better serve to bring out the significance 

 of Discontinuity in Variation to the general theory of Descent, it 

 may be well to choose some examples with reference to characters 

 which when seen in domestic animals are looked on as especially 

 the result of Selection. 



In exoskeletal structures several of this kind are known. 

 From time to time there have been records of captures of the 

 " hairy variety " of the Moorhen (Gallinula chloropus), in which the 

 feathers were destitute of barbules and consequently had a hairy 

 texture, greatly changing the general appearance of the bird. 



Of the " hairy " variety twelve specimens were recorded, five from 

 Norfolk, and the rest from Cambridgeshire, Hampshire, Sussex (2), 

 Suffolk, Nottinghamshire and Athlone in Ireland. The tips of the 

 barbs and shafts of the feathers have been broken off and the barbules 

 are entirely wanting, giving a hairy appearance. This appearance was 

 found in the whole of the plumage. Owing to the absence of barbules, 

 the general coloration is tawny. A few feathers of this kind have 

 been found in Hawks and Gulls, and in the case of a Parra (a bird 

 which bears considerable resemblance to a Moorhen), lent to Mr Gurney 

 by Professor Newton, a great portion of the body feathers were in this 

 condition. The feathers of the Apteryx and Cassowary are also partially 

 destitute of barbules. Mr Gurney was informed of a single case of a 

 Grey Brahma hen which shewed the same peculiarity which appears 

 otherwise to be without parallel. The case of the Silky Fowl is 

 similar in the absence of most of the barbules, but in it the point of 

 the shaft is produced to a delicate point, and the barbs are tine and 

 sometimes bifid or tritid at the apex. From J. H. Gurney, Trans. 

 Norwich Nat. Soc, in. p. 581, Plate. [Bibliography given.] [Tf 

 another " hairy " Moorhen is found, note of the colour of the skin and 

 bones should be made, for, as is well known, in the Silky Fowl they are 

 purplish blue.] 



The following may be compared : " Cochins are now and then met 

 with in which the webs of the feathers having no adhesion, the whole 

 plumage assumes a silky or flossy character like that of the Silky Fowl. 

 It usually occurs quite accidentally, and in every case we have met 

 witli, the variety has been Buff. By careful breeding the character 

 can be transmitted, but we have only known <>,<>> case in which there 

 had been this hereditary character, the others having been of accidental 

 occurrence. Such bircls are sometimes called 'Emu' fowls." Lkwis 

 Wright, IllvM. Book of Poultry, 1886, p. 230. 



Of many domestic animals, for example, the goat, eat and 



rabbit, varieties with long, silky hair are familiar under the name 



of "Angoras." Very similar breeds of guinea-pigs are kept, to 



which the name " Peruvian " is given. In this connexion the 



capture of a mouse {Mm musculus) with long, black, silk-like hair 



is interesting 1 , as shewing that such a total variation may occur 



as a definite phenomenon without Selection. 



1 Cocks, W. P., Tram. Cornwall Polytech. Soc, L852. Like other animals, 

 mice have of course often been found black. For instance, a number of black mice 

 were found in Hampstead-down Wood. Hkwktt, Y\\. '/.oo\. Jour. iv. p. 348. 



