244 EVOLUTION AND DISEASE. 
usually attached to hairs, but may occur in situations © 
where hairs are not found normally. A number of tubu- 4 
lar glands may be collected together and give rise to a_ 
compound organ like the kidney; in the same way a 
collection of racemose glands may form a compound 
organ, such as the salivary glands, or the poison glands 
of snakes. In complex animals like vertebrata, glands 
of peculiar character are restricted to definite parts of 
the body. Thus sebaceous glands are almost peculiar to 
the skin ; mucous glands to mucous membrane, and so 
forth. Thus it comes to pass that there are frontier lines, 
and as a rule these lines are not violated. For instance, 
at the lips the territory of sebaceous glands ends and 
that of mucous glands commences. At the termination 
of the large bowel or rectum, a similar condition of things 
exists, Lieberkiihn’s follicles so characteristic of the 
bowels terminate. Numerous frontier lines of this nature 
exist in our bodies. Another fact of considerable im- 
portance is that at birth an animal is not furnished with 
all the glands it will require, the germs of many arise 
in after-life and even subsequent to the years of active 
growth. Inthe chapter on supernumerary mamma, it 
was pointed out that in recesses of skin or mucous mem- 
brane glands grow luxuriously, and to this may be added, 
especially if the recess is moist. 
In young individuals we find occasionally in connec- 
tion with a functional gland, a tumour which when 
examined microscopically displays all the features pecu- 
liar to the gland with which it was connected ; the only 
point in which it differs is that the adventitious mass is 
impotent, that is, it cannot produce the secretion peculiar 
