338 
POPULAR SCIENCE REVIE'W. 
Echinodermata began to seek outside alliances with the worms, 
just as the Coelenterata are now anxious to annex the Spongida. 
As long ago as the days of Edward Forbes, when the Radiate 
sub-kingdom was flourishing, that great naturalist paved the 
way to a late favourite zoological development. In treating of 
one of the great divisions of Echinodermata, the Sea Cucumbers, 
or Holothuriadse, he introduced a group of creatures which he 
called Vermigrade Echinodermata, such as the shell-bearing 
Sipunculus and the Spoon Worm. He wrote, “In the animals 
of which we have now to treat, Radialism sets and Annulism 
appears. In their external appearance they are worms, for the 
likeness they bear to the Holothuriae (Sea Cucumbers) depends 
on a correspondence with the vermiform and not the radiated 
character of those animals ; but internally they afford evidence 
of belonging to the same great class. They are in fact Annelidous 
Radiata.” This idea bore fruit, and set a fashion, and the 
attempts to unite the Echinoderms with the worms, gave way to 
attempts to make worms of the whole set. The Sipunculidse 
and their allies were, however, put into the Vermes, and now rank 
as Grephyrea ; but other discoveries led the urchins, five-fingered 
jacks and their fellow hard-skins within the domain of the worm 
for awhile. 
The embryology, or rather the changes of form of the young 
Echinoderms, was studied by Muller. And it became evident 
from his admirable work, that not only was the Radiate type 
non-existent in the early stages, but that there was then an 
evident two-sided symmetry ; the young stage approaching, for 
a time, the immature forms of some worms. The alliance of 
the Echinoderms with the worms was not, however, left where 
Forbes placed it. Naturalists insisted on the union of the two 
groups, and thus the hard-skins were, for a time, united to a 
very disjointed group, possessing all sorts of anomalies of 
structure on account of so many of its members being parasites. 
Commonplace naturalists did stare when such things as wheel 
animalcules and tape-worms were united ; but having got used 
to it, they ceased very much to wonder when Huxley united 
these and the whole of the Echinodermata in a primary 
category of the animal kingdom under the head Annuloida. 
All have a water-vascular system, there is two-sided symmetry 
in all, and their ciliated larvae are not without resemblances. 
Macalister, of Dublin, however, says, “ the Annuloid arrange- 
ment is a convenient though unnatural grouping, as the 
Echinoderms are Deuterostome^, whilst most of the worms 
(Scolecids) included in Annuloida are Archaeostomatous.” The 
meaning of this appears to be, that in these worms the original 
embryonic mouth remains during life, but that in the Echino- 
derms, this original opening having served its purpose, does not 
