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as Infusoria flagellata. 207 
stratum, the faint yellow spicula (fig. 64, sp, sp!) are imbedded 
in systematic order, and overlap each other irregularly in two 
or three layers. ‘They present two diverse forms—namely, a 
simple aciculate shape (sp!) and a stellato-triradiate (sp) one. 
The rays of the latter are slender, tapering duathaoary to a 
bifid termination, divergent at equal angles from each other, 
and lie in the same plane. Without exception they are all 
arranged with one ray (often longer than the others) projecting 
backwards, 7. e. away from the excurrent orifice, and the other 
two extending symmetrically right and left, and obliquely 
transverse to the longer axis of the branch. In this manner 
they are disposed in a sort of network over the whole colony, 
even close up to the excurrent orifices; and as the aciculate 
spicula lie parallel with the rays of the other kind, there are 
‘consequently no projecting spines specially devoted to guard- 
ing the entrance to these apertures. 
he ostvoles (fig. 64, 0), or incurrent channels, are very nu- 
merous, there being at least two, and often three, opposite to 
every interstice of the spicula. They are very small, but quite 
conspicuous, especially at their inner ends, where they plunge 
through the monadigerous layer (md). ‘They afford great as- 
sistance whilst studying the contractile vesicles and the action 
of the flagella, since they enable one to get a freer view of the 
monads in an undisturbed state than where they are observed 
through all the tissues. It should be mentioned, however, in 
this connexion, that the profile-view (fig. 41) of the monads 
was obtained by making an actual section of one of the younger 
branches and allowing it to revive and expand in a fresh sup- 
ply of sea-water. , 
The monadigerous layer (figs. 41,64, md) lines the cavity 
of the body; and it is by the combined action of the vibrating 
flagella (#/) of the monads that currents of water and floating 
_ particles are kept up. ‘This layer is composed of monadiform 
animalcules (md), packed closely side by side in a vast colony, 
which extends over the whole length and breadth of the ge- 
neral mass. In this respect we are reminded of the similar 
arrangement of the individuals of that floating Ascidian, Pyro- 
soma. 'These monads crowd so closely upon each other that 
their sides are mutually compressed, and they thus form a sort 
of irregular polygonated pavement (fig. 64, md). They all lie 
with the anterior end (f) turned inwardly and projecting into 
the general cavity, and the posterior extremity imbedded in 
the cytoblastematous, shetipriak general envelope. 
The body of a monad is yellow when seen by transmitted. 
light, and in general terms may be designated as broadly oval, 
with the longer axis extending antero-posteriorly. Behind it 
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