Fewkes.] 
112 
[Dec. 5, 
my theory is impossible. The evidence afforded by the form of the 
spines that they are adapted for paddles seems to render it plausible 
that in some ancestor they may have served for propulsion. Nor is 
the fact of the early appearance of these structures without a bear- 
ing on the subject of their phytogeny. Consider the fact that these 
nectospines form very early in the development of the starfish. 
When they first appear there is no indication of the stellate form 
of the body. The brachiolaria has not begun to be absorbed and 
there are but eleven of the calcareous plates of the future starfish 
formed. If the early appearance of structures means anything in 
ontogeny, certainly these early formed bodies have some story to 
communicate in regard to the relationship of the starfish. I sug- 
gest that they are homologous with structures which, if we knew 
the ancestry of the starfishes, would be found to exist as organs for 
swimming in some now unknown genus. This interpretation of 
the function of structures with which these primarily formed spines 
are homologous is but a suggestion, but as far as I know it is the 
only one yet proposed. 
While we ma}^ possibly interpret these early formed spines of 
Asterias as survivals of swimming organs we certainly cannot sup- 
pose that certain hook-shaped structures early developed in certain 
ophiurans play the same physiological role, nor have they the 
same forms. The common features which they share are simply 
their early appearance, their large size, their limitation as a gen- 
eral rule to young larvae, and their differences from the perma- 
nent spines of the adult. Before we consider these spines in ophi- 
urans, let me call attention to a significant difference in the manner 
of origin of the primary spines and the true spines of Asterias^ 
which points to a radical difference in these two structures. It has 
been recorded that some of the spines of the starfish originate as 
extensions from the plates already formed, when the starfish spine 
is not formed from a separate centre of calcification. This seems 
to be the only way certain immovable spines on the abactinal sur- 
face of the starfish could form a priori when they simply appear as 
tubercles from the plates. There are, however, many spines on the 
abactinal plates, as for instance those found on the dorsals which 
are formed from separate calcifications. The primary spines al- 
ways arise from separate calcifications as Ludwig has shown in As- 
terina 1 and as I have described in Asterias . 2 We may then suppose 
1 Op. cit. 2 Op. cit. 
