80 



what we said of \Saccocrinus, Ctilicorrinus and Megistocrinus 

 may be said with equa' force of Blairocrinus, Sampsonocrinus, 

 Shumdrdocrmns, Andricocrinua, Baiocrinus, and Dorycrimis. If 

 this manner of reasoning is at all admissible, with what show can 

 we say that from Genmrocrimis arose Aciinocriiius and Amphora- 

 crinus? Is it not the merest guess upon the most remote possibity? 

 The theory of evolution does not mean that animal life was con 

 tinually improving in any or all of the channels of its existence, 

 nor that it was declining when not improving. Neither did it pass 

 through cycles from the embryo to senility, in genera, families, 

 orders or classes. On the contrary, if of any value as a theory, 

 the evolution must conform to what we find in nature, and that 

 is almost ceaseless change, without necessarily involving advance- 

 ment or decline; but conformability^ with environment and sur- 

 roundings. And wfc do not find what we call advancement or a 

 higher degree of development, neither do we find a decline or 

 degradation, in the family of the Actinocrinidiv, from its appear- 

 ance in the Upper Silurian, to its disappearance, in the St. Louis 

 Group. Nor do we find any development to a higher or decline 

 to a lower stage of existence, in any of the genera or species, 

 (hiring all that period. The species are the most abundant in the 

 Burlington Group, and the variations within specific limits, are 

 more numerous there than elsewhere. And, having fixed upon 

 certain characters, which we call specific, we observe, where species 

 are most abundant and fruitful, the greatest tendency to break 

 over these lines, so as to leave it doubtful, sometimes, whether 

 a particular form should be regarded as a variety of a described 

 species or as a distinct species. This occurs among the il/< yisto- 

 crinus, in the Hamilton Group, and among the Baiocrinus, in the 

 Burlington and Keokuk Groups; but we do not see in it any 

 progress toward senility of the species or the reverse. [u fact, 

 we do not know whether ornamentation of the test indicates 

 strength or weakness. We do not know whether Megisiocrinus 

 ornaUis with its delicate sculpturing is in a higher or lower stage 

 of development than 3f. spinosulns, with its canopy of spines; 

 nor whether Batorrinus nodulosiis, with its probosci.s, ornamen- 

 tation and tumid plates is in a higher or lower stage of develop- 

 ment than B. ohlalus, with plane, smootii plates and no proboscis. 

 We do not know whether B. oblatiis with its twenty-two arms 



