944 DIVISION II. MOLLUSCOUS ANIMALS.—CLASS IV. ACEPHALES. 
the water which has entered the body by the posterior, so that its motion 
is always retrograde, whence it has happened that some naturalists have 
mistaken the posterior aperture for the real mouth. It also generally swims 
with the back undermost. The cloak and its envelope exhibit in the sun 
the colors of the rainbow, and are so transparent that the whole structure 
of the animal can be seen through them: in many they are furnished with 
perforated tubercles. The animal has been seen to come out from its 
envelope without apparently any injury. But a more curious fact in their 
history is that, during a certain period, they remain united together, as they 
were in the ovary, and float in the sea in long chains, the individuals being 
disposed, however, in a pattern different in different species. MM. de Chamisso 
assures us that he has ascertained a still more singular fact, which is, that 
the individuals that have issued from a multiplicate ovary have not an ovary 
of the same kind, but produce only isolated individuals of a form considerably 
different from their originals; and these, again, give birth to others with 
ovaries similar to the parents of the first, so that there is, alternately, a 
generation of separated individuals, and a numerous generation 
t= 
scanty 
of aggregated individuals, and these two alternating generations do not 
resemble each other. These animals are found in abundance in the Medi- 
terranean and the warmer portions of the ocean, and are frequently 
phosphorescent.” 
The second family — Ageregata — of this order is composed of animals 
united ina common mass, so that they seem to communicate organically 
with each other. This union, however, does not take place in the early 
stages of their existence, but at a later period. 
Borrytius. —The Botrylli have an oval form, adherent to various 
foreign bodies, and are united by tens or twenties, like the rays of a star. 
They form gelatinous crusts bespangled with stars on the leaves of alge. 
Every star-ray is the body of one of the individuals of which the extraordi- 
nary colony is composed; and in the centre lies the common intestinal 
orifice. 
Pyrosoma.— The Pyrosome unite in great numbers, so as to form a 
large hollow cylinder, open at one end and closed at the other, which 
swims in the ocean by the alternate contraction and expansion of the 
individual animals composing it. They sparkle during the night with 
all the brilliancy of phosphorus. 
The two remaining classes of this division, — the Brachiopods, or arm- 
footers, and Cirrhopods, or beard-footers, have nothing interesting to 
offer, and we therefore pass them by without further notice. 
