900 



SCIENCE 



[N. S. Vol. XXV. No. 649 



direction." Rather than mutation Ortmann 

 looks to isolation as the important factor and 

 summarizes his position as follows: 



1. The normal case is when two closely allied 

 species, possessing identical or nearly identical 

 ecological habits occupy separated areas, which lie 

 close together but do not overlap. * * * 



2. Whenever allied species are found in one and 

 the same locality (overlapping), isolation becomes 

 apparent in the following forms: 



{a) The two species have different centers of 

 origin, that is to say, they were separated form- 

 erly, but occupied the same territory subse- 

 quently. * * * 



(6) If the centers of origin are more or less 

 identical (absolute identity is hardly possible), 

 the two species always differ ecologically, and 

 although living at the same localities, prefer dif- 

 ferent surroundings. * * * 



So much for the general results of Ort- 

 mann's investigations, but such an outline 

 does not throw into the foreground some of 

 the features of the work which deserve special 

 mention. This paper is devoted to the fauna 

 of a limited area, and contains several of the 

 elements which go to make up an ideal treat- 

 ment of a local fauna. Not only is there an 

 abundance of detailed facts, supplemented by 

 a critical review of former records, but a very 

 serious attempt is made to understand the 

 meaning or significance of the details pre- 

 sented. Thus Ortmann's efforts to interpret 

 and correlate the mass of facts is particularly 

 commendable and is a marked departure from 

 the usual annotated lists. He sees clearly that 

 many of the facts to be explained involve a 

 knowledge of the conditions which formerly 

 existed and consequently he turns to a study 

 of the determining conditions. The present 

 work is also an important lesson on the value 

 of a knowledge of the ecological relations of 

 animals in the study of their relationships 

 and geographical distribution, and clearly il- 

 lustrates the difference between the older 

 ' orthodox ' zoogeography and the newer eco- 

 logical phase. 



Some suggestions may be mentioned which 

 offer opportunities for improvement or expan- 

 sion in future work. While the details of the 

 environment of the burrowing species are de- 

 scribed fully, the same information is needed 



for the brook and river habitats; and such 

 descriptions can be supplemented to advantage 

 by photographs of representative situations. 

 We need detailed maps showing the occur- 

 rence of crawfishes, in a manner similar to the 

 mapping of plant societies by ecological bot- 

 anists. The composite system of mapping 

 used is not very satisfactory and would have 

 been greatly improved had fewer species been 

 placed on the map, and still more, if topo- 

 graphic maps had been used as a base. 

 County and stream names are of great ad- 

 vantage on maps devoted to detailed faunal 

 studies, and especially when the details of dis- 

 tribution are not expressed on the maps. 



Ortmann does not seem to recognize, in 

 more than a general way, the need of formu- 

 lating the conditions which compose the most 

 favorable (optimum) habitat, so that through- 

 out the geographic range of a species the 

 modifications of the habitat may be followed as 

 definitely as structural and functional modifi- 

 cations (habits, etc.), so that eventually per- 

 haps such relations may be correlated. In 

 this connection it should be mentioned that 

 the ecological observations are very largely 

 from western Pennsylvania and should be ex- 

 tended over a larger area. But to do this the 

 necessary time for field study as well as for 

 collecting must be available. The importance 

 of the laws of habit, habitat and environ- 

 mental change is so great that it is very de- 

 sirable that field students and institutional 

 authorities see the real importance of these 

 studies. 



While reading this memoir a need has been 

 felt for definite criteria by the aid of which 

 some estimate could be made of the degree of 

 primitiveness or specialization of forms. Fur- 

 ther, if the general bearing of mutation is to 

 be tested or used to the best advantage in the 

 interpretation of the problems of habits, habi- 

 tats and geographical distribution (of both 

 plants and animals), it seems necessary to 

 formulate criteria by means of which muta- 

 tions can be recognized in nature (at least 

 with some degree of probability), without re- 

 course to pedigree cultures. Here, as when at- 

 tempting to determine centers of origin, great 

 care is necessary to avoid arguing in a circle. 



