HAIRS OF MONOTREMES AND MARSUPIALS. 585 



level, i.e. closer to the surface, they will coalesce completely to form a common 

 follicular opening through which the hairs emerge. 



Fig. 7. — Transverse section across a large flattened hair of an adult Echidna. 

 There is no dorsal thickening of the cuticle, or restriction of pigment to the 

 lower surface. The hair is from the dorso-lateral aspect. 



Tig. 8. — Transverse section across a large flattened hair of an adult Echidna, 

 from the ventral surface just behind the bill. The anterior face is distinctly 

 concave. This form of hair is especially developed in specimens of Echidna 

 from Central Australia, and has not been noticed on specimens from Tasmania, 

 Victoria, or Queensland. 



EiG. 9. — Longitudinal section through the follicle of an embryo Ornitho- 

 rhynchus on the chest region. The nuclei at the base of the follicle are slightly 

 elongate. There is no trace of a dermic papilla. Zeiss, apert. 0"95, oc. 4. 



Fig. 10. — Longitudinal section througli a follicle at a slightly later stage 

 from the same embryo of Ornithorhynclius in the chest region. At this stage 

 there is the earliest appearance of a modification in the dermis (d.p.) to form 

 a dermic papilla, up towards which a small blood-vessel runs (d.v.). Zeiss, 

 apert. 0"95, oc. 2. 



Fig. 11. — Longitudinal section through a follicle of the same embryo of 

 Ornithorhynchus from the back just in front of the tail. The slight swelling 

 indicating the future sebaceous gland (s.ff.) is seen; below this the follicle is 

 slightly swollen, and at the base a flat plate-like structure {/.p.) is formed, 

 which has been slightly pushed in by the developing dermic papilla, a and 6 

 indicate the future lowest part or rim of the bulb. In the centre of the follicle 

 the nuclei are arranged with their long axes roughly parallel to that of the 

 follicle. Zeiss, apert. 0"95, oc. 1. 



Fig. 11«. — Transverse section across the base of the follicle at the same 

 stage as Fig. 11, to show the flat plate with its elongate nuclei. 



Fig. 12. — Longitudinal section through the same stage in an Echidna 

 embryo, to show the flat plate at the base of the follicle. Tiiere is no ap- 

 pearance as yet of the development of the sebaceous gland, the follicle being 

 probably at a slightly earlier stage of development than the one represented in 

 Fig. 11. Zeiss D, oc. 1. 



Fig. 13. — Longitudinal section through the follicle of an embryo of Echidna, 

 showing the early formation of the bulb and the upgrowths of the dermic 

 papilla. At the external end of the follicle are two swellings (s. A. ?) which 

 may possibly indicate outgrowths to form the follicles of small hairs. The 

 nuclei within the follicle are arranged in lines following roughly the length of 

 the follicle. At the bulb end the nuclei are more definitely arranged, and 

 there is the earliest indication of the upgrowths to form the hair rudiment 

 itself, but as yet there is no pigment present and no cornification. Zeiss, 

 apert. 095, oc. 2. 



