584 BALDWIN SPENCER AND GEORGINA SWEET. 



EXPLANATION OF PLATES 44—46, 



Illustrating Mr. Baldwin Spencer's and Miss Georgina Sweet's 

 paper on '' The Structure and Development of the Hairs 

 of Monotremes and Marsupials." 



List of Eefekence Letters. 



A. Point at which the cuticle of the hair is continuous with that of the 

 inner root-sheath, b.v. Blood-vessel, c.h. Cuticle of hair. co.h. Cortex of 

 hair. d. Dermis, d'. Special modification of dermis in Echidna to form an 

 enclosure for the group of follicles, d. p. Dermic papilla, f.p. Plate-like 

 structure at the base of the solid follicle, h. Hair, h^ Tip of developing 

 hair in follicle. i. r. s. Inner root-sheath, i.r.s^. Equivalent of Henle's, 

 andi i. r. s^, oi Huxley's layer. I. h. Large hair, m.'p.g. Stratum Malpighii. 

 o.r.s. Outer root-sheath, s.g. Sebaceous gland, s.h. Small hair. st.c. 

 Stratum corneum. st. I. Stratum lucidum. 



The outlines of all the figures are drawn under the camera lucida. 



Pig. 1. — Transverse section across a group of hairs from the back of an 

 adult Platypus, showing four groups of small hairs. The left side lies at a 

 deeper level than the right side, where in one group all the root-sheaths have 

 coalesced to form a common follicle. In the other groups the sheaths of the 

 different hairs are distinct. There is no successional large hair, Zeiss, 

 apert. 0-95, oc. 1. 



Pig. 2. — Transverse section across a group of hairs from the back of an 

 adult Platypus, showing six groups of small hairs. The root-sheaths of all the 

 hairs are distinct, Zeiss D, oc. 1. 



Pig. 3. — Transverse section across the shield part of an adult large hair of 

 Platypus. The distinct flattening is seen, and also the dorsal thickening of 

 the cuticle, and the bilateral arrangement of the pigment in the ventral part 

 of the cortex, nearer to which side lies the medulla. 



Pig. 4. — Transverse section across a group of hairs lying to the side of the 

 mammary area in an adult female Echidna. The large hair lies anteriorly. 

 Each hair has its distinct outer and inner root-sheath, and the follicles are bound 

 together into a group by a special deeply staining modification of the dermis. 



Pig. 5. — Transverse section across a group of hairs lying on the ventral 

 surface just behind the bill of an adult Echidna. A large flattened hair and 

 six small hairs are present. The inner root-sheath is especially well de- 

 veloped. There is no distinct medulla to be seen. 



Pig. 6. — Transverse section across a group of hairs from the mammary area 

 of an adult female Echidna. No large hair is present. The section lies close 

 to the surface, and shows the root-sheaths coalescing. At a slightly higher 



