Ses set | 
ee es Oe ROPES Swi epee eT 
ee ee a ee pS, 
a 
a ee Ee ee ee eee, ee ee ee ae ee ee ae a a SS. a. aes ere ee er 
— . “ sigs e ee 6 ie i g : 
C. F. Liitken on Ophiurans. 59 
gested food from the mouth. The side plates of the arm carry 
the arm-spines (spinae laterales vel brachiales). These are arranged 
in sets, and, at the pleasure of the animal, may be raised from 
the arm, depressed, with their points outward, and spread and 
closed like a fan. They are placed either along the outside border 
tooth-like papilla of Ophioderma to the long glossy, thorned 
spine of Ophiothriz. As to their arrangement in the vertical 
ju spines diminish in number but increase in proportionate 
ength. 
Growth of Ophiurans. 
The variations which the Ophiuran is subject to, from the time 
it leaves the egg till the gcd ce ot emerges from the larval con- 
dition, are explained in Joh. Miiller’s most admirable investiga- 
tions of the metamorphoses of the Echinodermata. In 
to the variations it undergoes, after the metamorphosis has taken 
place, we know little or nothing, except that these variations are 
not unimportant. ‘The serpent-star does not appear completely 
finished on emerging from its larval form; when newly born 
and rambling about on the surface of the water, it is not more 
like the full grown animal, than a young opossum is like its 
parents. We may see perhaps, that they belong to one or the 
other of the Ophiuran series, but, as to the species, we can only 
ar at it from the locality or abundance of the specimens. 
ven in the half grown animal there are still such variations 
from the adult form that the identity might be doubted were not 
the intermediate steps known. It is therefore plain, that the 
description of a species is not full, until several ages of that 
species have been properly illustrated. The following table will 
show approximately some changes which take place during the 
— of Ophiopholis aculeata (Ophiolepis scoiopendrica). The 
iameter of the dise, the length of the arms, the number of joints 
