SINGLE-COIIB MINORCA AND WHITE-CRESTED POLISH. 9 



teste Hagenbach) and has been studied by Blumeubach (1812), Hagenbach 

 (1839), Tegetmeier (1856), Darwin (1876), and others. A dome rises from 

 the front of the nasal bone often to a height of 15 or 18 cm. (figs. 7, 10, 

 PI. II). This dome is the secondar}^ bony covering of a cerebral hernia 

 whose dura mater has become ossified. .Such cerebral hernias are not un- 

 common among poultrj'. Roughly, i per cent of the chicks (outside of the 

 crested races) that failed to hatch in my incubations and were examined by 

 me had such a hernia. In one or two instances Polish chicks that died 

 before hatching were affected by incomplete closure of the cerebrum, the 

 top of the head not being covered by bone or skin. Such an abnormality 

 has been described by Hagenbach (1839, pp. 324-326) also. So profound a 

 modification of the brain would naturally be associated with mental pecul- 

 iarities. My own Polish have shown themselves very slow of movement, 

 and two male Houdans (having the same sort of abnormal skull) were 

 affected by some trouble in the head which led them to move backward, 

 turn somersaults, and move otherwise abnormally. Hagenbach .states that 

 the Polish fowl are subject to apoplexy and epilepsy. It is remarkable 

 that formerly the hens alone had the cerebral hernia (Darwin, 1876, Chap. 

 VII), while now it occurs in both sexes. 



4. Crest. — This consists of a number of large white feathers arising from 

 the frontal region of the skull (figs. 1,2, and 7). Structurally, they, like 

 normal feathers from the top of the head, have the barbules of the distal 

 portion of the barbs reduced so that the barbs do not interlock. This con- 

 dition is seen in the hackles of all breeds. The form of the feathers resem- 

 bles that of the hackle, being more attenuated in the male than the female. 

 The great size of the crest feather, like that of the hackle, is largely due to 

 its long period of growth. After molting, the new crest feathers are char- 

 acterized by long and stout sheaths in which the feather develops. These 

 persist after most of the other contour feathers no longer possess sheaths 

 and consequently have stopped growing. 



The cause of the crest is a matter of much interest. Hagenbach (1839, 

 p. 329) raises the question and says : 



Nicht ohne Bedeutuag scheint mir iibrigens eine auf die Hemicephalie beziigliche 

 Beobachtung von Meckel* zu sein, welche so lautet : " .Sehr merkwiirdig ist die haufig 

 vorkommende regelwidrige starke Entwicklung von Haaren an ungewohnten Stellen. 

 So fiude ich bei einigen voQ deneii, welche ich vor mir habe, und gerade bei denen, wo 

 der Hauptmaiigel am grossteu ist, fast den ganzen Korper, besonders aber den Riicken, 

 die Hiiften und die obern Extremitiiten, mit Haaren von 6 Linien bedeckt." 



Whether or not the developmental disturbance is the cause of the pro- 

 longed growth of feathers, it is certain that the immediate cause is the 

 unusual and prolonged nutrition of the feathers. The skin from which they 

 arise is thick and rich in blood-vessels. Whether the cerebral hernia is a 



* Handbuch der pathologischen Anatomic, Tom. I, p. 195-260. 



