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XIX. On the Structure and Development of Myriothela. 
By Professor Allman, M.D . , LL.D ., F.B.S., President of the Linnean Society 
Eeceived February 5, — Read February 11, 1875. 
GENERAL DESCRIPTION. 
Mykiothela, of which we have as yet no satisfactory evidence of more than a single 
species being known, consists of a solitary attached hydranth, carrying near its proximal 
or attached end the blastostyles or appendages which give origin and support to the 
gonophores (Plate 55). 
Full-sized specimens (fig. 1) measure, when extended, nearly 2 inches in length. 
They are then cylindrical in form, with the mouth occupying the summit of a short 
conical hypostome, behind which the tentacles commence, and thence extend over 
somewhat more than one half the entire length of the body ; while the proximal end of 
the body is bent at right angles to the rest, is invested with a chitinous perisarc, and 
gives origin to short sucker-like processes of attachment. 
For some time after the animal has been removed from the sea and placed in the con- 
finement of our jars, the tentacles will present the appearance of short papilliform pro- 
cesses (fig. 3). This condition, however, is that only of the tentacles in a state of 
contraction. When fully extended their form is very different; for they then attain a 
length of nearly half a line, and present a thin cylindrical stem, terminated by a large 
spherical capitulum, very well defined and distinct from the stem (fig. 2). In this 
state the tentacles are kept in constant motion, the animal perpetually depressing them 
and elevating them with a peculiar jerking action. 
The tentacles are very numerous ; upwards of two hundred may be counted in a 
single hydranth. For the greater part of their extent they are set close to one another; 
but as they approach their proximal limit they not only become smaller, but are sepa- 
rated from one another by greater intervals. Almost every tentacle carries a small 
purple pigment spot on its summit. 
The hydranth when contracted (fig. 3) becomes club-shaped or conical, and the 
tentacles then pass into the state of short, thick, imbricated papillae. 
The contractility of the hydranth exists chiefly in the tentacular portion. In all that 
portion which carries the gonosome the contractility is much less marked. In the ten- 
tacular region the contractility is shown not only in the great extent to which this part 
of the hydranth can elongate and shorten itself, but in the loops and contortions, like 
the writhings of a worm, into which, when fully extended, it frequently throws itself 
(fig. ii). 
MDCCCLXXV. 4 D 
