5 2 
THE NATURALISTS’ JOURNAL. 
mollusc, with its mantle-secreted shell, to the Vertebrate classes, 
in which scales were commonly found among the fishes and rep¬ 
tiles, a soft unprotected skin among the Amphibia, feathers 
among birds, and true hairs among mammals, the last two forms 
of skin-appendages being characteristic of each of the two 
classes respectively. The feathers of birds were of two kinds, 
the soft downy feathers of the body and the hard and stiff wing 
and tail-feathers, which, by offering resistance to the air, enabled 
the bird to fly. Not only this, but the barbs of the wing feathers 
locked into one another and formed a still stronger resisting 
medium when the bird gave a stroke with its wing in flight. 
Among the mammals, the pangolins and armadillos offered cur¬ 
ious modifications of the skin appendages, being covered with a 
hard scaly armour which very effectually protected them from 
their enemies. The spines of the porcupine served the same 
purpose in another way. The prolongation of the skin into flying 
membranes was seen in the bats and flying squirrels. The horn 
or the rhinoceros was, as shewn by the microscope, made up of 
agglutinated hairs. Woman’s hair, in the lecturer’s opinion, was 
the most wonderful, and cases of its reaching over six feet long 
were given. The human skin then received attention. The true 
skin, or cuticle, was the sensitive one, and lay beneath an outer 
covering, the epidermisor “scarfskin,” which was an extravasation 
of the true skin, and entirely destitute of nerves and bloodvessels. 
These two layers were again divided into several more complicated 
ones, according to the form of the cells of which they were com¬ 
posed. Numerous tiny projections, or papillae, were found in 
sensitive parts, especially the soles of the feet and the palms of 
the hands, and had a special grouping of the nerves running into 
them, forming a “ plexus.” To illustrate this the audience were 
treated to a view of a portion of the lecturer’s own thumb, seen 
under a high power of the microscope. The formation of the 
skin, as known bv the researches of a German, was as follows :— 
From the blood (liquor sanguinis) was thrown out a lymph, in 
which certain bodies named “ cytoblasts ” were developed; these 
rapidly grew by feeding on the lymph, and became spherical 
cells, pressing on one another and ultimately forming a layer. 
Other layers formed beneath, and the older cells were throw off, 
and this process continued all through life. Going on to hairs, the 
lecturer showed that they were not as popularly supposed 
hollow tubes, but that their interior was filled up with the medulla 
or pith. They were lubricated by an oilv fluid, secreted by the 
sebaceous glands, which were so situated that they poured their 
contents on the outside of each hair. 
Mange in dogs was caused by a tiny Arachnidan, the same as 
the parasite living in little pimples on the skin of the human 
subject, as had been proved by experiment ; the name of this 
animal was Demodex folliculorum. Some verv beautiful insect 
