PROFESSOR YVYVILLE THOMSON ON THE ECHINODERMATA. 413 
The form of the body changes to a four-sided prism, the anterior 
surface separating from the posterior, and thus forming the lateral 
surface, which at first are pretty regular. Shortly the border curls 
up, so that a hollow is formed on either side ; and, beyond this point, 
Dr. Busch was unable to pursue his observations. No ciliated fringes 
were as yet defined on the surface of the zooid. 
V.—“Vermiform Larva.” 
37. This form was observed by Professor Muller at Nice, in the 
summer of 1849. It was ^ of a line in length, and slightly nar¬ 
rower ; annulose in appearance with four transverse furrows dividing 
the dorsal surface into five segments. The second and third segments 
were the largest; the first and last were extremely minute. The 
dorsal surface was opaque and brownish with patches of dark pig¬ 
ment. The ventral surface, as far as the fourth segment, was colour¬ 
less, and shaped like a five-rayed star. Ten long colourless vascular 
coeca were arranged symmetrically, a pair on each ray, evidently the 
first row of ambulacral feet. The dorsal transverse grooves termi¬ 
nated on the ventral surface in the angles between the rays. The 
dorsal perisom was supported by a close network of calcified tissue, 
and on the ventral aspect there was the usual pentagonal ring of oval 
plates. The posterior segments projected behind the star. The centre 
of the last segment presented a slight depression, but Muller was 
unable to determine with certainty whether there was an opening in 
this position. # 
CL* 1) * 
Bather further developed, the dorsal surface had assumed the 
form of a pentagonal disk, and a soft appendage, probably a respira¬ 
tory tentacle, projected from each of the salient angles. Muller de¬ 
scribes individuals still farther developed, which he observed at Trieste 
in the autumn of 1850, but they show no change of special interest. 
38. I shall now briefly state the general conclusion to which I have 
been led by the careful study of the various aspects of this singular 
process. 
The only character which all the Asterid germs appear to possess 
in common, is the fusion of the whole, or of a part, of the germ-mass 
* Vermiform larva of a star-fish—«. ventral, b. dorsal aspect. (After Muller.) 
