422 MERISTIC VARIATION. [part i. 



Metacrinus. Some species have normally 5, others normally 8 radials. If there 

 are 5, the 2nd and 3rd are united by syzygy and bear pinnules; but if there are 8, 

 both 2nd and 3rd, and the 5th and 6th are thus united and bear pinnules. In 

 Plicatocrinus the number of radials is tivo, and this is also the case in one or two 

 fossil Comatulas. Pentacrinus has normally three radials like Antedon. 

 629. Pentacrinus miilleri: specimen having in one ray four radials, the 2nd and 3rd 

 united by syzygy, though bearing no pinnules. Carpenter, I. c. ; and Chall. Rep. 

 xi. Pt. xxxn. p. 311, PI. xv. fig. 2. 



(1) that the number of individuals that have lost antennae — a serious injury one 

 may judge— and have renewed them, and have bred, can have been enough to lead 

 to the establishment by Selection of a distinct and highly special device to be 

 invoked solely on the occasion of mutilation of an antenna ; and also (2) that the 

 least detail of normal form is of such consequence as to be rigorously maintained by 

 Selection. 



