58 THE FEMALE GENERATIVE ORGANS. 
Describe the structure of a seminiferous tubule and the tissue 
about it. 
These tubules are quite long when unravelled. They lie in a loosely- 
arranged connective tissue containing many bloodvessels and cells of 
various forms, some of which may be pigmented. The tubules havea 
well-defined basement membrane upon which the lining cells are 
placed, several layers thick. When in a state of rest the cells upon 
the basement membrane or membrana propria are large, granular and 
well defined, having a distinct nucleus. Upon this layer lie two or 
three layers of small nucleated cells with poorly-defined cell-bodies. 
Among these cells, when they are in a state of activity, are seen bundles 
of spermatozoa with their tails projecting into the lumen of the semin- 
iferous tubules. The spermatozoa are believed to be formed from the 
cells in the outer layers. 
What is the structure of a spermatozoon ? 
It consists of a pear-shaped body called the head. To the large 
end of the head is attached a slender filiform process called the tail. 
Between the two and next to the head is a short segment called the 
middle piece. 
What is the structure of the vas deferens ? 
It is a thick, walled tube surrounded with a coat of smooth muscle 
tissue, the outer layer of which runs in a longitudinal, and the inner 
layer in a circular, direction. It is lined with a mucous membrane 
covered by a layer of cylindrical non-ciliated epithelium. 
THE FEMALE GENERATIVE ORGANS. 
VAGINA. 
Of how many layers is. the vagina composed, and what is the 
structure of each ? : 
Three. An outer fibrous layer composed of fibrous connective 
tissue with elastic fibres in it. A middle layer made up of smooth 
muscle cells arranged longitudinally and circularly, and an inner layer, 
the mucous membrane, made up of loose connective tissue containing 
elastic fibres. The mucous membrane lies in folds or ridges and is 
covered with a layer of stratified epithelium. It has in its deeper 
portions venous plexuses, which give it the appearance of erectile 
tissue, 
