In this article we will discuss about the external morphology of volvox.
1. Coenobium (a colony with definite number of cells) is a hollow sphere of mucilage made of many cells.
2. All the cells are arranged in the periphery of mucilaginuous sphere in a single layer (Fig. 15).
3. Number of cells in a colony varies from 500 to 60,000 in different species.
4. Cells are connected with each other by the cytoplasmic strands, which form a net-like structure in the colony (Fig. 16A, B).
5. All somatic cells are green in colour and show a typical Chlamydomonad structure, i.e., similar to that of Chlamydomonas. Cells in Volvoxglobator are Sphaerella type.
6. Each cell remains surrounded by its individual mucilaginuous sheath.
7. Two flagella of equal length are present in each cell.
8. Two to six contractile vacuoles are present in each cell (Figs. 16, 17).
9. A single nucleus, cup-shaded chloroplast, with one or more pyrenoids and an eyespot are also present in each cell.