586 BALDWIN SPENCER AND GEORGINA SWEET. 



Fig. 14. — Longitudinal section through the follicle of an embryo Ornitho- 

 rhynchus. The rudiment of the hair can be clearly seen arising from the bulb, 

 faint but distinct lines being pi'esent, which converge towards the apex of the 

 hair rudiment and separate series of nuclei from one another. Pigment has 

 appeared, and stretches up towards the medulla. The follicle is solid, but at 

 the external end the nuclei are beginning to dip in towards the centre. The 

 gland is well developed, and reaches as far down as the level of the tip of the 

 dermic papilla, which is not shown in the drawing. The stratum corneum 

 is continuous over the top of the follicle. Zeiss apert. 0"95, oc. 1. 



Fig. 15. — Transverse section just above the level of the tip of the dermic 

 papilla of a follicle at a sligiitly later stage than that represented in Fig. 14. 

 The layers of nuclei indicating the cuticle of the hair (c. h.) and of the inner 

 root-sheath {c.i.r.s.) can be seen. Outside these li« the inner root-sheath, 

 which is commencing to be corneous {i. r. s.), and the outer root-sheath (o.r.s.). 

 Zeiss F, oc. 1. 



Fig. 16. — Transverse section through the same follicle as the one repre- 

 sented in Fig. 15, at a higher level. In the centre lies the solid follicle in 

 which the large hair is being developed. Anteriorly is the gland, and on 

 either side a follicle, budded off from the central one in which the first formed 

 small hairs will be developed. Zeiss F, oc. 1. 



Fig. 17. — Longitudinal section through the follicle of an Ornithorhynchus 

 from the dorsal surface of an embryo at a later stage than that represented in 

 Fig. 14. The hair has grown up, through the corneous network into which 

 the inner cells of the follicle have been modified, as far as the point /^j. The 

 cornified inner cells form the inner root-sheath, which tightly encloses the 

 growing hair and stains deeply. At the upper end an irregular lumen is de- 

 veloped leading to the exterior. The inner root-sheath is directly continuous 

 with the stratum lucidum of the epidermis. In the bulb region the layer of 

 nuclei continuous with the cuticle of the hair (c.k.), and with the cuticle of 

 the inner root-sheath, can be distinguished (c.i.r.s.). Only the proximal 

 part of the now well-developed sebaceous gland {s.ff.) is indicated. Zeiss, 

 apert. 0'95, oc. 1. 



Figs. 18 — 20. — Transverse sections across the follicle of the same embryo 

 as represented in Fig. 17. 



Fig. 18. — Section at the level of the tip of the dermic papilla. The cells 

 filled with pigment, and representing the medulla and cortex, lie next 

 to the dermic papilla. The cuticle of the hair (c. h.) and of the inner 

 root-sheath (c. i. r. s.) are clearly seen. Outside the latter lie the nucleated 

 layers of the inner root-sheath, and outside this the outer root-sheath 

 (o. r. s.), which is very thin in this part and consists of two layers of 

 cells, the nuclei of the outer layer being large and deeply stained, and 

 those of the inner layer very few in number and smaller. Zeiss F, oc. 4. 



