174. Mr. A. Hancock on the Anatomy of the 
be done. Indeed so complete are the results of this naturalist, 
that, perhaps, the publication of my own may appear almost un- 
necessary. My investigations, however, carried on as they have 
been perfectly independent of the researches of others, may not 
be without some value even where novelty is wanting. Micro- 
scopic investigations conducted by the aid of transmitted hight 
are liable to error. Frequent examinations in such cases are 
therefore necessary, and observations independently prosecuted 
are of peculiar value. Consequently I do not hesitate to give the 
result of my own labours on this subject, fraught as it is with 
difficulty, not fearing to mislead in a path already so well trodden. 
Of the anatomy of these animals I shall have to confine myself 
almost entirely to that of Plumatella, Fredericella and Paludicella. 
Of Alcyonella I can say but little, having seen only an imperfect 
specimen, and none of the other freshwater forms have come 
under my notice. 
Plumatella and Fredericella resemble each other very closely in 
their anatomical structure, notwithstanding the external differ- 
ence of their polypes. Paludicella however shows some very in- 
teresting modifications, particularly in the muscular system: but 
before entering on the internal anatomy it will be necessary to 
examine the characters of the polypidom, and to trace its rela- 
tionship to the polype. 
The polypidom of Plumatella Allmani, Pl. V. figs. 8, 4 & 5, 
and of Fredericella sultana is tubular, branched and carinated on 
the upper surface; the walls opake, tough and membranous, in- 
clining to horny. Those of the latter, when examined through 
the microscope, exhibit a sort of dendritic structure ; the divisions 
or branches passing in an irregular spiral direction round the 
tube, are flattened, and extensively anastomosing form for the 
most part a dense tissue, nowhere more open than just to display 
the branched character. The walls of Plumatella do not in the 
least exhibit this structure. In Paludicella the polypidom, fig. 2, 
is likewise branched and tubular, but not carinated ; it is mem- 
branous or horny, and becomes enlarged and contracted at cer- 
tain intervals, dividing the whole, as Gf were, into cells or com- 
partments, the external surface beg smooth and very glossy. 
All these genera have the polypidom lined with a delicate 
membrane—the tunic, Pl. IL]. figs. 46,6 & 54, and Pl. IV. 
fig. 1b, which is attached only at certain points to the inner sur- 
face of the external tube or cell-wall. This in Plumatella and 
Fredericella becomes excessively delicate towards the orifice, where 
it apparently blends with the tunic. But in Paludicella the union 
at this point of the horny wall and tunic cannot be mistaken, 
though the blending is so gradual that it is impossible to say 
where one ends and the other begins. And when this polype is 
