88 The Study of Animal Life part i 



which the parents alone are concerned), maternal (in which the 

 mother is the head of the family), and paternal (in which the male 

 becomes prominent). But higher than the pair and the family is 

 what Espinas calls the "peuplade," what we usually call the 

 society, whose bonds are, for the most part, psychical. 



But let us consider this problem of the evolution of 

 sociality. The body of every animal — whether sponge or 

 mammal — is a city of living units or cells. But there are 

 far simpler animals than sponges. The very simplest 

 animals, which we call firstlings or Protozoa, differ from all 

 the rest, in being themselves units. The simplest animals 

 are single cells ; each is comparable to one of the myriad 

 units which make up a sponge, a coral, a worm, a bird, a 

 man. 



Here, therefore, there is an apparent gulf. The simplest 

 animals are units — single cells ; all other animals are com- 

 binations of units — cities of cells. How is this gulf to be 

 bridged ? It is strange that evolutionists have not thought 

 more about this, for on the transition from a unit to a com- 

 bination of units the possibility of higher life depends. 



Every higher animal begins its individual life as a single 

 cell, comparable to one of the firstlings. This single cell, 

 or egg-cell, divides ; so do most of the Protozoa. But when 

 a Protozoon divides, the results separate and live in- 

 dependent lives ; when an egg- cell divides, the results 

 of division cohere. Therefore, the whole life of higher 

 animals depends upon a coherence of units. 



But how did this begin ? What of the gulf between 

 single-celled Protozoa and all the other animals which are 

 many-celled 'i Fortunately we are not left to mere specula- 

 tion. The gulf has been bridged, else we should not exist ; 

 but, more than that, the bridge, or part of it, is still left. 

 There are a few of the simplest animals which form loose 

 colonies of units, which, when they divide, remain together. 

 Whether it was through weakness, as I am inclined to 

 believe, that the transition forms between Protozoa and 

 higher animals became strong, or for some hidden reason, 

 we do not know. Some speak of this coherence of 

 firstlings as a primal illustration of organic association, 



