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mind that the immediately investing sac has the power, in almost every case, 
of secreting from its external surface a secondary investment of very various 
constitution in the different groups ; and we may, moreover, conceive of the 
entire animal with its digestive tube, tentacula, ganglion, muscles, generative 
organs, circumambient fluid, and investing sacs, repeating itself by gemma- 
tion,* * * § and thus producing one or more precisely similar systems, holding a 
different position relatively to one another, while all continue organically 
united, and we shall then have the actual condition presented of the Polyzoa 
in their fully developed state.” 
Now of these two investing tunics, the outer one is called 
the ectocyst, the inner the endocyst.f This latter tunic hues the 
interior of each chamber, and terminates in the tentacular 
crown (lophoplLoreX) ; it is transparent, and is readily seen in all 
the Fresh- water Polyzoa, both when the animal is protruded, and 
when it is retracted within its cell ; for a portion of the endo- 
cyst always remains “ in a permanent^ invaginated state.'” The 
ectocyst, in most of the genera, consists of a tough leathery sub- 
stance, imbedded in which are silicious and other earthy particles. 
In Fredericella I have noticed that the sihcious “ trustifies,” 
or component cells of Diatomacece, especially those of Diatoma 
vulgare, enter largely into the composition of the ectocyst ; Cris- 
tatella alone appears to be destitute of an ectocyst. The in- 
habitant of each cell is called a Polypide,§ a term wisely pro- 
posed by Allman instead of Polype, which should now be con- 
fined to the animals belonging to the Radiata ; the whole 
dermal system of a colony is known by the name of ccencecium. || 
The very curious valve-hke organ, like a tongue, which arches 
over the mouth, and which all the fresh- water species, except 
Paludicella, possess, has received the name of epistome .^[ The 
presence or absence of this organ, whose function, by the way, 
it is difficult to determine, gives the name of the order to which 
the numerous species respectively belong. Those Polyzoa 
which are furnished with a bilateral tentacular disc, and whose 
mouth is provided with the tongue-like organ described above, 
are placed in the order Phylactolcemata ,** to which are referred 
all the fresh- water species, except Paludicella, and none of the 
marine except Pedicellina ; while the species destitute of an 
epistome, and which have a circular tentacular crown, belong 
* i.e., Budding. 
t Ectocyst , from the Greek ectos, “ outside,” and cystis, a “ bladder,” or 
“ bag.” Endocyst, from endos, “ inside,” and cystis. 
J From lophos, “ a crest,” and phoreo, “ I bear.” 
§ From polypous, “ a polype,” and eidos, “ resemblance.” 
|| From coinos, “common,” and oicion, “ a house.” 
IT From epi, “ upon,” and stoma, “ a mouth.” 
** From phylasso, “ I guard,” and laima, “ the throat.” 
