96 How Animals Changed 



2. Animals Running or Jumping on Ground: aniphibians, perioph- 

 thalmids, coenobitas. 



3. Animals Living in Ground: Phycosoma, Lycastris, nemerteans, 

 earthworms. 



b. Actively Homoiosmotic Animals with Well-developed Skin Organs 

 to Prevent Desiccaton (chitin, horn, imbedded glands) : dry air 

 animals which are more or less independent of relative humidity. 



1. Flying Animals. 



2. Animals Living on the Ground. 



3. Animals Living in the Ground. 



c. Animals which have Secondarily Returned to Water: 

 L Damp Air-Breathers: limnaeids. 



2. Animals which have Secondarily taken to Water-breathing: 

 many pulmonates, siphonarians, Ancylus, oncidies, ephemerid 

 larvae. 



Integument 



The chief functions of animal integuments are protection from 

 blows and parasites; insulation against desiccation and loss of heat; 

 respiration; excretion; regulation of body temperatures; and regula- 

 tion of interchanges between body fluids and the surrounding me- 

 dium. In general the skins of terrestrial animals are thicker and 

 less permeable than those of aquatic animals (Hesse, 1920; Noble, 

 1929; Harms, 1932). Thus they more effectively prevent desicca- 

 tion and protect internal organs. Many of the animals that live in 

 the ocean have an integument which permits free interchange be- 

 tween body fluids and the surrounding medium. Some marine ani- 

 mals and those that live in fresh water are able to maintain their 

 body fluids at concentrations which differ from the media in which 

 they live. Certain aquatic animals and most land animals are little 

 influenced by the surrounding medium, even when they are wet 

 continually by rains or immersed in water. 



Wardlaw (1931) says, "Far from tending to isolate themselves 

 more completely from their surroundings, the most perfectly adapted 

 organisms are those in which the freest interchange is allowed with 

 the environment." There may be some question as to what "perfect 



