Page:Insects - Their Ways and Means of Living.djvu/362



finest matter consists of great quantities of minute grains (d) floating about separately or adhering in irregular masses. Besides these etements there are many droplets of oil (e), recognizable by their smooth spherical outlines and golden-brown color. The fat cells are mostly irregu- larly ovoid or elliptical in shape; their protoplasm is filled with large and small oil globules, and contains also masses of fine granules like those floating free in the blood. These granules are the protoplasmic substances formed within the fat cells. Many of the cells have irregular or broken out- lines (b, c), as if their outer walls had been partly dis- solved, and the contents of such cells appear to be escap- ing from them. In fact, many are clearly in a state of dis- solution, discharging both thëir oil globules and their pro- teid inclusions into the blood; and it is clear that the similar matter scattered so profusely through the blood liquid has come from fat cells that have already disin- tegrated. All these materials will gradually be consumed in the building of the tissues of the adult, the organs of which are now in process of formation. In Chapter IV we learned that every animal consists of a body, or soma, formed of cells that are differentiated from the germ cells usually at an early stage of develop- ment. The function of the soma is to give the germ cells the best chance of accomplishing their purpose. An insect that goes through two active forms during its life, a larval and an adult form, differs from other animais in having a do«ble soma. The entire organism, of course, is hot double, for, as we have just seen in the study of the caterpillar, many of the more vital organs are continuous from the larva to the adult; but there is a group of organs which, after reaching a definite form of development in the larval stage, at the end of this stage virtually die and go into dissolution, while a new set of tissues develops into new organs or into new tissues replacing those that have been lost. The groups of somatic cells that-form the tissues and organs that undergo a metamorphosis, there-

[304]

THE