PLUMULARIANS. 
229 
but the gap between this and the common pattern is bridged 
over by intermediate forms. In yet another section, the pinnae 
are shortened, and carry only a single calycle and hydra, and 
here again the feathery character is less distinct ; but the loss 
in this respect is compensated for by other elements of beauty. 
A single species of this section ( Plumularia obliqua) is found 
on our shores, a fairy-like form of exquisite delicacy and grace ; 
and, strange to say, it is equally at home at the Antipodes. I 
have masses of Australian algae over which it spreads in extra- 
ordinary luxuriance, as though the habitat were thoroughly con- 
genial to it. From the same region I have obtained another 
and very remarkable form (still undescribed) which is referable 
to this section. Other sub-divisions of the Plumularian family 
are founded, as I have said, on differences in the reproductive 
system, with a single exception, to which I shall refer more par- 
ticularly hereafter. The principal varieties in external aspect 
have now been noted, and it will be seen that the main features 
of form and habit are strongly marked, and very constant 
throughout the tribe. 
I proceed to notice some very interesting points of structure, 
which are peculiar to this family and have no parallel amongst 
recent hydroid zoophytes. Allusion has frequently been made 
to the “ calicetti,” which occur on the Plumularian colonies, in 
addition to the calycles in which the hydras are lodged. They 
exhibit various forms, being sometimes tubular (PI. CXI., 
fig. 4) and sometimes cup-shaped; they sometimes consist 
of a single chamber and sometimes of two chambers, placed 
one above the other. In the latter case the lower portion 
is tubular (PI. CXI., fig. 5), while the upper expands into a 
hemispherical bowl ; the whole may be compared to a goblet on 
a stand. These curious appendages are, like the calycles, an 
extension of the horny covering which invests the whole of the 
common flesh of the hydroid. In one section of the family 
their disposition is invariably the same ; two stand out laterally, 
one on each side of the calycle, and one, which is often of con- 
siderable length, is adherent to the front of it, and has the 
appearance of supporting it like a bracket (PI. CX., fig. 6). 
In the other section there is no such uniformity of arrange- 
ment ; the “ calicetti,” which are here of the cup-shaped type 
(PI. CXI., fig. 3), are distributed, often profusely, over the 
colony, in the neighbourhood of the calycles, along the course 
of the pinnge, on the central stem, and even at times on the 
creeping fibre. They are very useful to the systematist, sup- 
plying him with good criteria for the discrimination of species. 
But their chief interest lies in the nature of their contents. 
When examined in the living state, they are found to inclose 
an offshoot from the common flesh, or rather from the outer- 
