Mac 



Mic 



From General to Special 



to the group repre- 

 sented by the hydra, 

 from the hydra to sev- 

 eral types of " worms," 

 from worms to the 

 jointed-legged animals 

 like insects and spiders 

 and lobsters, and so 

 on to the backboned 

 group. These facts 

 do not of course 

 tell us that there has 

 been any genetic con- 

 nection between the 

 simpler and the more 

 complex types, a 1 - 

 though they are in har- 

 mony with the suppo- 

 sition that there has 

 been transformation of 

 species. 



A division o f 

 labor, in the sense in 

 which this expression is 

 applied to living things, 

 is to be expected only 

 after there has been a 

 certain amount of in- 

 tegrating or bringing 

 together of units, and is 

 therefore more pro- 

 nounced in larger or- 

 ganisms than in the 

 microscopic forms. 

 Nevertheless, even the 

 one-celled animals, 

 among their thousands 



87 



Cv 



Fig. 21. DiPLODiNiuM ecaudatum 



This one-celled animal lives in the stomach of 

 cattle. In addition to the long macronucleus 

 (Mac), the small micronucleus (Mic), and the 

 contractile vacuole (Cv) commonly found m pro- 

 tozoa, this animal has a distinct anus (a), a skeletal 

 support (S), an oesophagus, sensory tracts, motor 

 bundles, and other structures corresponding to 

 special organs or tissues of highly complex animals. 

 Adapted from R. G. Sharp. 



