Volvox in South Africa. 559 



Entity and Interdependence of the Volvox Cell. 



The vegetative cells of a Volvox colony are interdependent and 

 intimately united with one another by the protoplasmic connecting 

 strands. Yet they retain their individuality each is in itself a 

 complete individual in so far as its own immediate life-processes are 

 concerned ; it absorbs, manufactures food, initiates movement, etc., 

 but it has lost the power of further division or of reproduction. Yet 

 it is possible for it to continue existence if separated from its sister 

 cells, although this separate existence is very short-lived. 



If the colony is slightly crushed by pressure on the cover-slip it is 

 sometimes possible to separate the vegetative cells, or rather the 

 protoplasts, more or less completely without injuring them. Such 

 naked protoplasts may continue moving in an aimless way for some 

 time. Eelieved from mutual pressure and strain, the protoplast 

 alters in shape, becoming an elongated pear shape with rounded 

 base, all angles disappearing, so that it looks not unlike a form of 

 Chlamydomonas. Such separated cells may be seen in Plate XLV, F, 

 mixed with free sperms from which they are distinguished by their 

 larger size, large chloroplast (stained dark by iodine), and rotund 

 shape ; one shows a very large eyespot at the apex. 



Change in Appearance of the Vegetative Cells. 



As the colony ages, the appearance of the cell network constantly 

 alters. At first the closely packed cells form a dense green network, 

 which often appears as though built up of a number of green 5- or 

 6-rayed stars united to one another by the points of the rays (Plate 

 XIII, B). 



As the distance between the protoplasts increases, the connecting 

 strands become more and more drawn out, the green colour disappears 

 from them entirely except just at the broad base, the protoplasts 

 themselves become smaller and paler with ill-defined chloroplasts, 

 and the whole network is very fine, with delicate attenuated meshes 

 connecting the small nodes (Plate XIX, D, E). The pyrenoids grow 

 smaller, and highly refractive globules of volutin or other metabolic 

 substances, as well as the contractile vacuoles, become proportionately 

 more conspicuous. Since the eyespots in the anterior cells do not 

 change, in such old colonies they show up very clearly. 



Thus it is possible to judge of the age of an individual colony by 

 inspection of the vegetative cells alone, irrespective of the state of 

 the reproductive cells or the size of the colony. 



