‘520 CLASS ECHINODERMATA. 
small tubes, which they construct with foreign molecules, 
but which make no part of their body, like those of the 
polyparia. Their rotatory organ, nevertheless, appears out 
of the tube, pretty nearly after the manner of the head of the 
polypi. 
We have one common enough on the conferve of our 
marshes. Vorticella tetrapetala, Blumenb., Dutrochet. Ann. 
Mus. xix. xviii. 1—10, whose rotatory organ is divided into 
four lobes. 
BRACHIONUS, Miill., 
With rotatory organs, and a tail pretty nearly similar to 
those of the furculariz, carry a sort of membranous, or 
scaly buckler, which covers their back, like that of certain 
monoculi. 
SECOND ORDER. 
INFUSORIA HOMOGENEA, 
Whose body exhibits neither viscera, nor other complications, 
and often does not even present any appearance of a mouth. 
The first tribe 
Comprehends those which, with a gelatinous body, more 
or less contractile in its various parts, still presents as external 
organs, some ciliz more or less strong. 
They are named URCEOLARIA, Lam., when they have the 
form of a trumpet, from which the ciliz issue, as in the polypi 
called Vorticelle ; 'TRICHOD#, when with a flat body, these 
cilie are at one extremity; LEUCOPHRA, when they sur- 
