HAIRS OF MONOTREMES AND MARSUPIALS. 569 



seen separating the nuclei into series which converge towards 

 the point of the growing hair. These lines of nuclei become 

 more definitely outlined as development proceeds, and are 

 associated with certain definite parts of the hair and root- 

 sheaths, to which reference will be made later. The gland at 

 this stage is very clearly marked, and its nuclei are all small, 

 round, and take the stain deeply. The outline of cells can be 

 seen in parts of the gland (though not as yet in the hair 

 follicle) ; and though there is no opening to the exterior there 

 are traces towards the base of the gland of an internal cavity. 

 Though the follicle is quite solid there is in both the stratum 

 lucidum and stratum corneum an indication of the formation 

 of a lumen. The nuclei begin to dip down towards the central 

 line of the follicle, as indicated in the figure; this is most 

 strongly marked in the case of the stratum lucidum, the outer 

 layers of the stratum corneum still running continuously over 

 the spot where will subsequently be the opening of the lumen. 

 A transverse section across the bulb just above the level of the 

 tip of the papilla is shown in fig. 15. In the centre lie the 

 nuclei with pigment round them, continuous with those lining 

 the bulb on its inner surface. It will be seen that there is no 

 continuation upwards of the cells of the dermic papilla. This 

 part of the hair probably corresponds to both the medulla and 

 the cortex. Then follows a circle of six nuclei of considerable 

 size, which represent, we believe, the nuclei of the layer form- 

 ing the cuticle of the hair; outside these is an irregular circle 

 of smaller and more deeply staining nuclei, which, judging by 

 sections of later stages, represent those of the so-called cuticle 

 of the inner root-sheath ; outside these are one or more layers 

 of larger nuclei irregularly arranged and belonging to the 

 inner root-sheath, while the outer layer of nuclei represent 

 the outer root-sheath. The whole is enclosed in dermic tissue. 

 A transverse section at a level just below the origin of the 

 sebaceous gland is represented in fig. 16. In the centre lies 

 the follicle of the large hair, and at either side is the early 

 indication of the follicles in which the two first formed small 

 hairs will be developed. These, as shown in the next stage, 



