1888 .] 
Ill 
[Fewkes. 
naturally recalls the paddle-like spines of certain deep-sea echi- 
noids. The flattened spines are well shown in the genus Doroci- 
daris ( D . Blakei ) ? and as far as their form is concerned they seem 
admirably suited for serving as paddles. 
It is by no means necessary that we should suppose that these 
flattened spines serve in the young starfish or in the sea-urchin in 
which they are now found, for a locomotion of the animal from place 
to place. They may not, as the ctenopliore combs, the homolo- 
gous position of which with the spines is suggestive, serve as the 
only means of locomotion. We may suppose that they assist in the 
movements of the animals. The body of the echinoderm loaded 
with its heavy skeleton of calcareous plates cannot be raised by 
these organs serving by their action to offset the increased weight, 
but in conjunction with the legs they help in the onward move- 
ment. It is no new proposition that echinoderms move from place 
to place by means of flapping of parts of the body. Comatula can 
be seen to propel itself by a simultaneous movement of the arms 
and certain ophiurans are capable of a considerable onward move- 
ment by a rowing motion of their arms. In both these cases the 
amount of motion is limited and brought about by movement of 
the arms, while in neither case have the spines any particular mod- 
ification in form fitting them for a greater resistance upon the 
water. In the genus Ophiopteron, however, it would seem that 
these spines have developed paddle-like structures well adapted to 
assist in the propulsion of the animal in combination perhaps with 
movements of the arms . 1 
It appears that we might then interpret the peculiar, fan-shaped 2 
spines characteristic of the young starfish as survivals of a swim- 
ming organ, which has become functionless in the modifications of 
the body. While the body of the adult starfish, loaded with heavy 
calcareous plates, cannot be moved by these bodies, they still pre- 
serve a fan-shape which in an ancestral genus may have been of val- 
ue in locomotion. While this problematical ancestral free-swimming 
echinoderm is yet to be found this fact does not certainly show that 
1 These “ fins ” of Ophiopteron, following Ludwig’s description, are membranes sup- 
ported on ten rods, so that they might be regarded as compound bodies and not single 
spines. This would seem to prevent their homology with the solid single spines of As- 
terias. If we consider them homologous to the spines which support the “net of Pter- 
aster may they not be regarded as simple spines very much branched at the distal end ? 
2 I suggest the name nectospines for these structures to distinguish them from the 
older spines which are of uniform diameter. 
