268 THe Microscope. 
are the mucous and pus corpuscles, and the white corpuscles of 
the blood. 
At a bound, then, one passes from this low creature to the 
highest, to find that the tissues of the latter are but collections 
of the former. Soa tissue is chosen and with the aid of the 
knife and needles its parts are for a time successfully separated. 
But at last a period arrives when even this will not answer, 
and we turn to the microscope to find the tissue compounded of 
thousands of the smallest elements. To discover and to exam- 
ine these constitute the science of tissues, or histology. 
While the cell existed as an amoeba it acted in an inde- 
pendent manner, but now that it is in the service of a unity 
of cells it is a subordinate and must conform itself to its sur- 
roundings. 
Each cell in the body then is a living 
individual with an individual function. 
Some of these cells are very small, for 
it will soon be stated that five millions 
of them can be contained in a particle 
of the substance of the body no larger 
than a cubic millimetre. Some are so 
large that they are nearly, if not quite, 
Human ovum. a, vitelline .. - 
baembrane p. WieGs ©, ger- visible to the unaided eye. In shape, 
spots. also, there is the greatest variation. 
First, there is the spheroidal cell, from which the bodies of all 
the higher animal have proceeded, the ovum. As a result of 
compression and adaptation come other forms, from the slender 
cylindrical cell to the flat and scaly one. Still other cells 
appear with branched processes growing from their bodies in 
various directions. There exists, then, every variety of shape 
and form in the fully developed cells, although it will be stated, 
farther on that early in their history they were all alike, simple, 
undifferentiated bioplasm. 
Fig. 2. 
In a well-developed epithelial cell from the surface of the 
tongue two parts are readily recognized. First, the nucleus, a 
round or oval body, occupying a small part of the cell near or 
in its centre, and second, the part of the cell surrounding this 
nucleus. 
