IBS 
GENERA 
BELONGING TO THE SECOND ORDER OF THE THIRD 
CLASS. 
ANADYOMENA. 
A fan-formed Polypidom, with articulated and 
symmetrical nerves, almost transparent, and enve- 
loped in a gelatinous substance. 
As only one species is known to constitute this 
genus, it has long remained a doubt whether to class 
it with animal or vegetable productions : even the 
power of chemical analysis has been found insufficient 
to solve the difficulty, as many Thalassiophytes ap- 
pear to yield almost the same productions as this Po- 
lypidom ; nor does the microscope assist us in dis- 
covering any part we can consider as fructilicative. 
Analogy remains our only guide, and has induced me 
to place the Anadyomena among the animal creation. 
No marine plants, whether articulated or not, pre- 
sent the slightest resemblance in their organization 
to the object in question ; but that is not wholly the 
case with respect to Polypidoms, many of which are 
equally deficient in polypean cells. The substance 
of the Anadyomena, however, seems to be of the same 
nature as that of many of the Sertularias, andTubula- 
rias; it is much more horny than that of the Thalassio- 
phytes, and possesses a degree of stiffness and trans- 
parency which is common to some Polypidoms, but 
