470 the president's address. 



Take, for example, such a form as Nectalia or Physophora. 

 Here we have a large number of individuals or zooids attached 

 to a common stem. At the upper end a single modified in- 

 dividual forms a float. Along the length of the stalk two rows 

 of differently modified individuals form swimming bells, which 

 have concentrated their energies entirely upon the function of 

 locomotion, and have completely lost the power of feeding them- 

 selves and of reproducing their kind. At the bottom of the 

 stalk an expanded disc bears a number of other zooids. Some 

 of these have mouths and stomachs, and fishing tentacles 

 provided with thread cells, and their duty is to provide and 

 digest food, not only for themselves but for the entire colony. 

 Others, again, form protective shields or bracts, and yet others 

 bear the germ cells upon which the organism depends for 

 reproduction. 



This is, clearly, a very highly organised type of colony. 

 Whether, indeed, we should still call it a colony or regard it as 

 an individual of the third order is a debatable question, and 

 one which is of no vital importance, for we must remember that 

 it is impossible to draw hard and fast lines across the path of 

 evolution and say that all on one side of a given line is one thing 

 and all on the other side something else. 



At any rate, such colonies seem to have reached the limit of 

 their progress, and have not afforded any fresh starting-point 

 from which a new line of evolution has originated. 



There are, however, certain other Hydrozoa which exhibit a 

 type of colony formation that seems to foreshadow higher possi- 

 bilities. I refer to the common jelly-fish known as Scyphomedusae.' 

 The hydroid phase of these organisms forms temporary colonies 

 by a process totally different from branching. The entire 

 hydroid divides transversely into a heap of little jelly-fish or 

 ephyrae, resembling a pile of saucers. These remain together 

 for a while and form a kind of colony known as a strobila, but 

 presently they all separate and swim away. 



Amongst the coelenterates this process of strobilation is never 

 accompanied by any considerable differentiation and division of 

 labour amongst the constituent individuals of the colony, and 

 still less by integration, so that it leads to no higher type of 

 organisation. When we come to the worms, however, which 

 have undoubtedly arisen from coelenterate ancestors, we find in 



