WHEEL-BEARERS. 
201 
males of all the species have a very close similarity to each 
other. 
The females produce and deposit, one at a time, very 
large oval eggs, enclosed in a brittle shell. The young 
appear in the perfect form, being subject to no metamor- 
phosis, and for the most part with all their organs com- 
plete. In some of the lower forms, as Stephcmoceros, Me- 
licerta, <fec., the young are hatched in a grub-like condi- 
tion, from which the tentacles, disk, <fec., develop them- 
selves by gemmation. 
The genera jnst alluded to, and some others, are inca- 
pable of locomotion, except in earliest infancy ; tho young 
soon attaching themselves by the foot to some solid object. 
They now secrete and throw oil' from tho surface of their 
body successive coats of gelatinous mattor, which form an 
erect cylindrical case around them, into which they can 
wholly retire for protection, by contracting their fore parts 
on alarm. In general, this tube is simply gelatinous 
and transparent, except that it sometimes becomes par- 
tially opaque when old, by the adhesion to its exterior 
of Dialonacece, floccose particles, &c. ; but in one species 
( Melicerta ring ms), which hence becomes invested with a 
high interest, the tubular case is strengthened by a layer 
of solid pellets, manufactured by the animal for the occa- 
sion, and deposited, pellet by pellot, and layer upon layer, 
just like tho bricks in a piece of masonry. 
This species is one of peculiar beauty, and any of our 
young readers who possess a microscope, or have access to 
one, will do well to obtain an hour’s examination of it. 
Fortunately, it is by no means a rare animal in still waters 
where aquatic plants grow: the slender, much divided 
