Dr Allen Dalzell on the Colour of Hair. 329 



pelled and absorbed. 2. That in the Bird, the ovum, when 

 escaping from the ovary, is accompanied by the correspond- 

 ing vesicle — the ovisac; and that the ovisac becomes the 

 shell-membrane of the Bird's egg. 3. That the expelled and 

 lost ovisac in the Mammalia therefore corresponds to the 

 shell-membrane in the Bird. 4. That after the formation of 

 the ovum, the albuminous contents of the ovisac in the Mam- 

 malia correspond to the albumen in the Bird's egg. 5. That 

 the author's retinacula in the Mammalia, after all, find their 

 analogue in the chalazse of the Bird ; and that both have their 

 origin in the granular contents of the ovisac, which at an 

 early period are in appearance just the same in both. 6. 

 That the shell-membrane of the Bird is thus a primary cell. 

 He then points out the position which, from his observa- 

 tions, is to be assigned to the several parts of the ovum in 

 the language of " cells ;" and shews the presence of a plu- 

 rality of ova in a Graafian follicle to be referable to the same 

 cause as that producing more than one yelk (ovum) in the 

 Bird's egg. 



On the Colour of Hair. By Dr Allen Dalzell. Commu- 

 nicated by the Author. 



The colour of the hair, which, according to Griffith, was 

 long attributed to pigment accumulated in the cells of 

 the medulla, depends upon one or more of three causes. 

 First, on pigment granules ; second, on diffused colouring 

 matter impregnating the entire tissue ; and third, on the 

 presence of air spaces within the fibres of the shaft. To 

 these might be added the nuclei of the cells themselves, 

 which, however, where pigment granules are present, are so 

 surrounded by them, as to be scarcely, if at all, discernible. 

 But where their isolation has been effected by boiling with 

 moderately dilute caustic potash, they are shewn as dark 

 bodies of an elongated form. . 



The colour of the hair corresponds in intensity to that of 

 the iris ; as, for example, auburn with blue, and black with 

 the darker tints. Nor are these relations at all confined to the 



