The Message of Science. 31 



from the female cellules, except at time of fecundation, 

 when both colonies break up, scatter, and presently conju- 

 gate in pairs and groups. 



Colonies of protozoons which come from a single parent 

 cell present some analogy with a multicellular animal 

 organism, which also develops from a single egg-cell. 

 The way, however, from a colony of protista to the organ- 

 ism of a vertebrate animal is long and, in its setiology, 

 but little understood. 



The first metazoons were clearly temporary makeshifts, 

 owing to stress of accidental conditions. It is likely, 

 indeed, that thej' had often occurred for millions of years, 

 occurred thousands of times, but had died out, or pro- 

 gressed no further than the polyzoa we see at present 

 time, owing to unvarying conditions, flood and drought, 

 heat and cold. But at some time one or more of these 

 unions of cells chanced to survive longer and took more 

 permanent form, sufScient permanence to carry it on and 

 set up a new mode of life by organization — that organiza- 

 tion and difPerentiation of cell function which was to play 

 so grand a part in the future. 



Space and a desire to make the argument continuous 

 prevent more extended enumeration of such primitive 

 unions of unicellular life. But one has only to look abroad 

 on the face of nature to see conclusive proof of the posi- 

 tion here taken. In every tree, shrub, and plant,' in every 

 animal that walks, every bird and insect that flies, we 



