The system of transportation in animals developed grad­ually. When the particles of a live matter first joined together to form an independent unicellular organism and separated themselves from the ocean by means of an envelope, nature had to think of a way of organizing transportation within a unicellular body. A solution was soon found, and nature built the cell in the form of a microscopic ocean and provided it with its own currents. Thus, the simplest intracellular transportation system has been retained in multicellular animals and in man. The protoplasm of any cell in our body is mobile and protoplasmatic currents exist even in the nerve cells.

Multicellular animals had to develop a more complex system. The most primitive of them, for instance sponges, use the water where they live for this purpose. The ocean currents proved to be unreliable, so instead they use cilia to make the sea water flow through the ducts and pores of their body, thus supplying all parts with nutrients and oxygen.

Higher animals separated themselves completely from the ocean and provided themselves with their own ‘aquaria’ for transportation purposes. Nowadays the largest aquaria belong to the gastropod (univalve) mollusks, whose blood occupies 90 per cent of their body volume. This is evidently too excessive and the larvae of insects have an aquarium not exceeding 40 per cent of the weight of their body, whilst that of adult insects takes up 25 per cent. Birds and mammals have even smaller aquaria, only 7-10 per cent of their body weight, the tiniest reservoir being found in fishes where it is only 1.5-3 per cent of the body weight.

April 22, 2010 at 10:12 am by admin
Category: transportation system
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