ZOOLOG Y. 4I 
the union of five worms, the worms having united at their 
posterior ends, since the eyes are seen at the free ends of 
the star-fish. This interpretation of the structure of the 
star-fish is not without a parallel among the worms. The 
Botryllus, one of the sac-worms, is really composed of many 
little Ascidians living as one individual. There is nothing 
more extraordinary in five worms living together as a star- 
fish, than in many little Ascidians living together as a Botryl- 
lus. This view ofthe origin and the structure of the star-fish, 
first proposed by Haeckel, is in perfect harmony, according 
to the same author, with the facts of its development. The 
egg of the star-fish is transformed into:a larva, provided 
with an intestine from the inner part of the body of the 
larva. Around its mouth appear five distinct layers, which, 
uniting at their posterior ends, form the body and arms 
of the mature animal. The same kind of reproduction is 
seen in the Sipunculi, which are supposed to be indirectly 
the ancestors of the star-fish, and also in the Nemertian 
worms, from which, or their allies, the Sipunculi and other 
articulated worms have descended. Within a few years 
there have been found a very well-preserved group of fossil 
worms,—the Phractelminthes, or mailed worms. These are 
considered by Haeckel to be intermediate between the 
Sipunculus and the star-fish, they being scarcely distin- 
guishable from the arms of the latter. Through the union 
of worms, like the Phractelminthes, have the star-fishes 
been produced. The origin of the Asteridze, or star-fishes, 
from the worms, is in perfect harmony with the structure, 
development, and petrified remains of the group. The 
most striking facts of their economy are explainable on 
such a theory, but are perfectly meaningless on any other. 
The star-fishes are probably the ancestors of the remaining 
Echinodermata. Passing over the Ophiuridze, which differ 
but little from the star-fishes, we come to the Feather-stars, 
or Comatula (Fig. 43), which, when young, live in a 
