Classification of some colonial Chlamyclotnotiads. 15 
specimens of Pandorina; in all these the cells of the ccenobium 
were very rich in food reserves, and in some cases were under¬ 
going division. In all the others from one to four cells, usually 
grouped near one end, were very poor in food material, and were 
generally much smaller than the rest [Fig. 1]. In a few of the 
colonies the latter were undergoing division, whilst the few small 
Fig. 1 . Colony of Pandorina mortim with one sterile cell, S (reproductive 
cell, T). 
and hyaline cells were very contracted and may have been disin¬ 
tegrating. It is commonly found that division of the cells in 
Pandorina is not simultaneous; the case in which some of cells 
fail to divide at all are only extremes types, probably developed in 
relation to a restricted nutritive supply. 
The differentiation of vegetative and reproductive cells in 
Volvox, then, only represents a fulfilment of the general tendency 
towards division of labour. A parallel segregation of vegetative and 
reproductive cells has taken place in many groups of filamentous 
algae. Finally it is well known that heterogamy is the result of the 
same general trend of evolution in nearly all living groups. 
It will be seen, then, that we must turn to the cell structure 
in any attempt to classify the colonial Chlamydomonads. With the 
the exception of Volvo.x all the latter have a simple gelatinous cell 
wall, usually distinct from the common mucilage of the colony, but 
never showing a differentiated outer lumella as in Volvox [9, 13,20] 
and never with any protoplasmic strings traversing it. Hence these 
genera have the type of cell wall seen in the Chlamydomonadacese. 
o* 
