AT THE MICROSCOPE. 113 



Sarcoptcs scabiei, is parasitic on man, causing a very painful 

 pruriginous affection, well-known in some parts of the country by 

 the familar name of " The Scotch Fiddle." Another species 

 causes the affection called " Scab " in sheep ; the name of this is 

 '■'' Dtr?natodectes ovis." It proves at times a terrible scourge. One 

 species is found upon oxen, to which the name ^'' Symbiotes bovis''' 

 has been given ; it is nearly related to that before us, from the 

 Chaffinch, but certainly distinct. Birds appear to be peculiarly 

 subject to the attacks of these Itch-mites ; it is common to find 

 examples of two and three species on a bird, and I possess speci- 

 mens of five different kinds from one bird. 



TuFFEN West. 



EXPLANATION OF PLATES XXVIL, XXVIIL, 



Plate XXVII. 



Fig, 1. — Transverse section of Leaf of Yucca recurva. At the ends 

 will be seen the absence of Chlorophyll, to which a white stripy 

 appearance of the leaf will be due ; in the centre a line of 

 nourishing vessels, guarded by kidney-shaped bundles of 

 woody tissue. With a higher power will be seen on the 

 upper surface a good section of the dense cuticle, more highly 

 magnified in 



,, 2. — Ct., cuticle; sto., stomatal openings, guarded internally by 

 stomatal cells, stc. About the middle of the lower surface of 

 the section, a small portion of " ectoderm " has been broken 

 away, whereby we obtain a view of 



,, 3. — Stomata, st, of the outline of the cells at this part, and of the 

 papillte, J). 



,, 4. — The papilla3 are seen projecting, p.p. 



,, 6. — In a longitudinal section, raphid-bearing cells are to be seen, 

 and cut across in the transverse section (Fig. 5). 



,, 7. — A few long crystal prisms may also be seen. 



8. — Transverse section of Clematis vitalba : cZr. , corky layers of 

 bark ; l.f., liber-fibres ;p., pith ; m.r., m.r., medullary rays = 

 channels of communication between the central pith, and the 

 outer growing structures ; d. , ends of dotted ducts. 



9. — Portion more enlarged, showing corky layers of bark and 

 liber-fibres. 



K 



