ECOLOGICAL SUCCESSION. 341 



ecological significance. Take the piercing mouth parts of the 

 Hemiptera. This group occurs in every type of habitat from 

 the marine pelagic to the ectoparasitic, and from tundra and 

 desert to rain forest. All the chief principles of animal ecology 

 could probably be illustrated by the Hemiptera, the sucking 

 beak coming in only as a factor modifying the details, when we 

 compare Hemiptera with Coleoptera which have biting mouth 

 parts and similar habitat relations. 



Such doubtful protective devices, as protective coloration, 

 mimicry, aggressive coloration, etc., cannot be counted as any 

 significant part of ecology until they are first established in fact 

 and are shown to have some regular relation to reactions to 

 environic factors or at least to activity. All of the chief typical 

 cases that come under the head of protective coloration, mimicry, 

 etc., are much shattered by such facts as are presented by Selous 

 ('08, Ch. I. and II.). 



(b) Over-adaptation. If some animals are adapted, which 

 implies that they are adjusted to a particular mode of life in 

 their particular situation, in a way which is essential to a success- 

 ful life in that situation, then other animals are over adapted 

 (Coulter, '09, p. 62). Take an animal from the insect group, 

 the dragon fly nymph, which has the labium modified as a 

 prehensile organ and the maxillae as additional mandibles. The 

 posterior portion of the intestine is developed into a muscular 

 cavity containing gills and serving as an hydraulic organ of 

 locomotion. What is the advantage of all this specialization? 

 The nymph appears to succeed no better than many other types 

 with which it is in competition. It even appears clumsy and 

 unadapted in many ways and is to the same degree over-adapted. 



When we consider adaptations in relation to communities 

 of organisms and to physical environments, with taxonomy 

 thrown into the background, their significance loses force. 

 Adaptation is adaptation primarily, when viewed from the 

 standpoint of the structural type of the group to which the 

 adapted organism belongs; it is an index of taxonomic differentia- 

 tion rather than of ecological relations. The more important 

 structural adaptations appear to be adaptations to strata, or 

 matters of specificity. They have about the same significance 



