114 The Development Theory: A Review. 



cended from monkeys." With this object the writers have wisely 

 abstained altogether from indulging in theorizing or fine writing, 

 and have confined themselves to stating facts in the simplest lan- 

 guage, and leaving these facts to speak for themselves. 



The first chapter states the subject, setting forth the rival 

 theories of creation by evolution and by special act. In the 

 second chapter some of the most striking known cases of the 

 development of new species are quoted, and the imaginary nature 

 of the line between species and varieties is forcibly brought out. 

 We are tempted to quote one by way of illustration : 



" At Steinheim, in Wurternberg,* Germany, was once a small 

 lake, and its waters grew countless little shell-fish, many of them 

 water-snails like those of the rivers and lakes at the present day. 

 By the appropriation of the dissolved limestone in the waters of 

 the lake, generation after generation of these snails built up their 

 shells, only to let them fall to the bottom on the death of the 

 little inhabitant. By this slow process a layer of shell-mud was 

 formed, which has since hardened into chalk. About forty 

 distinct layers of this chalk may be distinguished, contain- 

 ing the perfectly preserved remains of many shells. And 

 now for the wonderful part of the story. The shells of each 

 layer remain much the same throughout its thickness, but 

 toward the limit of each, or before the beginning of the next, the 

 shells are observed to vary, so as to approach the form which will 

 be found in the next layer. And not only are the shells of the 

 lowest layer so different from those of the highest that if the 

 intermediate forms had not been discovered they would certainly 

 be called different species, but there are many among the 

 intermediate forms themselves which, if they had been found 

 separate from the others, would have been counted distinct 

 species." 



A diagram accompanies this extract, showing a gradual but 

 steady change of form from flat, discoid, planorbiform shells at the 

 base of the deposit to others with elevated spire at the summit. 

 iSo two of the series would probably pass as the same species 

 among conchologists, as every one acquainted with the fine 

 splitting prevalent among American Unios and Melanians will 



* Schmidt, Descent and Darwinism, pp. 97, 98. 



