223 Prof. F. J. Bell on the 
that this example may have had arms 400 millim. long, and 
a total spread of 800 millim., or something like 32 inches. 
The naturalist of an earlier school would have been con- 
tent to admire the delicacy combined with solidity of such an 
Ophiurid’s arm; today, when the current of speculation has 
set in a different direction, we are rather inclined to ask, what 
is the character of the struggle for existence of so large a 
creature, offering five distinct avenues for attack? The very 
condition of the injured specimen whose admeasurements have 
just been given answers the question; there must be a con- 
stant tendency to the loss of an arm or a part of one. 
Where vegetative repetition is so abundantly displayed, that 
loss can of itself hardly affect seriously the individual, cer- 
tainly not the species; but, in some cases, the danger may 
react on the species im this way: rather than part with 
an arm there may be a choice, due to an inherited ten- 
dency, in favour of a loss of individuality. The disk divides 
under the influence of attacks from without. 
The consideration of external influences is not, I think, to 
be neglected so completely as it has been by some writers. 
Simroth, for example, addressing himself to the ‘ Cardinal- 
frage,” “ob die Theilung der Seesterne tiberhaupt eine frei- 
willige sei, oder nur durch gewaltsame iiussere Hingriffe be- 
wirkt werde,” decides in favour of the former*; and Prof. 
Hickel, who even uses the epithet ‘ spontane,” writes, “ Bei 
gewissen Seesternen lésen sich die Arme freiwillig von der 
Scheibe ab” t. Ofcourse, nothing more is meant by “ volun- 
tary’ in this connexion than that the writer is unacquainted 
with the history of this tendency to fission, or with the cha- 
racter of the external stimulus that brings it into play. 
The well-known observations of Kowalevsky and others 
afford sufficient evidence of the phenomenon of what may, in 
a sense, be spoken of as voluntary fission; but it is obvious 
that in so saying we are not at the bottom of the matter, and 
that it is unphilosophical to seek for no explanation beyond 
that of the dictates of a free will. 
A capacity for self-injury appears to have been a dominant 
character in the primeval Echinoderm; the Holothurian of 
today can be easily roused to such a state of physiological 
excitement that he will eject his viscera ; so, it seems, under 
another form did the Astrophiurid stock retain this tendency. 
Under the influence of pain, fear, or anger, a starfish throws 
off an arm, or an Ophiurid divides its disk, fission of the disk 
* Zeitschy. f. wiss. Zool. xxviii. p. 421. 
+ Op, cit. xxx. (Suppl.-Bd.) p. 485, 
