272 ^ NEW YORK STATE MUSEUM 



the Stem alone, making the axis chosen for description the vertical 

 axis on the plate. A glance at figure 7 will perhaps show the 

 absurdity of considering this a normal position, particularly so if 

 the sigma plates bore spreading brachioles, as their structure sug- 

 gests. The posterior arm is usually the shorter and less developed, 

 the difference in environment caused by the position of the anus 

 being the probable cause.^ 



The plates of the type specimen, designated as A [pi. i, fig. 3,4] 

 are arranged as follows. There are three basal plates, the anterior 

 of which is about half the size of the others. This plate is in contact 

 with but two plates lying above it, while each of the other two is in 

 contact with four plates above. Numbering to the right from the 

 posterior margin, plate 4 rests on the upper left side of plate i, this 

 plate and the next are tetragonal and small; no. 6 is heptagonal, 

 large, and has a prominent and excentric umbo a little above and to 

 the right of the center; plates 7 to 9 are nearly as large as 6, are 



^I have for some years harbored a notion that one of the many laws under- 

 lying the production of variation and new species might be expressed by the 

 term, " the survival of the unfit," perhaps better stated as " the survival of 

 the weak," a law related to Cope's " law of the unspecialized." Failure 

 to divide normally at the proper time gave cell aggregates and inaugurated 

 a new wave in what Herbert Spencer points out as the law of rhythm in 

 evolution. No new crest of strength springs from the crest of the last wave 

 but each crest is preceded by a trough. The invagination of a weak hollow 

 sphere of cells gave rise to the gastrula and forced a division of labor on 

 the " unfortunate " aggregate ; and this law, if I may so call it, offers sug- 

 gestions as to the origin of many things from cell conjugation to the dis- 

 covery of some weak mortal that he might make the pen mightier than the 

 sword he was unable to use. The idea suggested a possible cause for the later 

 change in shape of Eunema epitome. Lyriocrinus? beecheri, 

 with its invaginated base produced at first by the yielding of weak basals 

 to the persistent attack of gravity, is an illustration in point and an extreme 

 is found in Blastoidocrinus carchariidens. The failure of 

 plates to support increased weight has initiated variation along this line in 

 many crinoids and natural selection has found certain mechanical advantages 

 in the new forms ; out of weakness has come strength. The law suggests 

 that ancestors of Malocystites were once supported by the stem alone and 

 had their arms in a normal position, but that descendants with weaTc stems 

 often found themselves let down to the ocean floor and had to make shift 

 to live under adverse conditions. Increased growth of the posterior plates 

 or decreased growth of the anterior plates would have brought the arms 

 again uppermost and given rise to a form like that here shown. A stem 

 unused for support might become of advantage as an organ of locomotion 

 and secure slow changes in position. 



