ORTMANN : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA oil 



(e) C. diogenes. 



C. diogenes is sharply separated from the other chimney -buildei-s, Ijut resembles 

 them ecologically to a certain degree. In Pennsylvania it comes into contact with 

 them, but in tlic case of C. carolimis this has been observed only once, while it is 

 more frequent in the case of C. monongalensU However, intermediate forms have 

 never been observed, so that we must assume that kyesamechania prevents crossing. 



In both cases, with reference to C. carolimis as well as C. vionongalemtis, it is to 

 be remarked that whenever one of these is found associated with C. diogenes it 

 is always only a contact, not a real mixing of both forms. Tiiis is best observed in 

 the case of C. vionongaleusis and C. diogenes. All over the range of C. viontrngalcnsis 

 in southwestern Pennsylvania C. diogenes is also found. But as has been stated 

 (p. 417 and 458), although they frequently dwell at the same localities they do not 

 occupy the identical locations, C. diogenes belonging to a lower level than C. vionmiga- 

 lensis. Thus we see again a separation, which isprirnarily expressed in the differenceof 

 altitude. Whether the latter is most important seems doubtful. It has been stated 

 that C. monongalcmis prefers spring-water, while C. diogenes lives mostly in swamps, 

 where the water is more or less stagnant and not so cool in summer. (Compare the 

 instance from Nine-Mile Run given above.) But, whatever may be the essential 

 feature which separates both species, it is clear that it is an ecological factor, and, 

 when these two species are found together, it is at a place where the ecological con- 

 ditions favorable to them come together. 



That C. diogenes depends on different ecological laws from C. mouongalensis is 

 also evident from the fact that the former has, outside of Pennsylvania, an entirely 

 different range. 



Thus we have here a case similar to that of C. bndoui when it associates with the 

 burrowing forms. Two allied species occupy (in Pennsylvania) almost the same ter- 

 ritory, and are not separated topographically, but their ecological .separation is evi- 

 dent, and very likely is connected with their specific diflerentiation. 



In tlie two laces C. diogenes, the eastern and western, we again see tlie influence 

 of separation. .Vccording to our tlR'ory that the area of C. diogenes was a unit in 

 Preglacial times, and that it was separated by the advancing ice into an eastern and a 

 western section, which subsequently remained separate, we must expect, if isolation 

 effects specific differentiation, that the eastern and western form of (.'. diogenes should 

 show at least a tendency to develop dillerential characters of specific value. This is 

 indeed the case, as we have seen above (p. 401 et seq). 



Isolation, or liabitudinal Segregation, as the factor forming species, is thus 

 clearl}' seen in every case discussed. Wo may condense the results obtained in the 

 following sentences. 



