SERTULARIA CUSCUTA OF ELLIS. 487 
Last spring I had the good fortune to find a small tuft 
of this Sertularia, which had been left on the beach by the 
tide, in the Frith of Tay, and at this place (Flisk), where 
the water is only brackish. Upon placing it in a glass of 
the Tay water, strengthened by the addition of a little salt, 
for the purpose of inducing the parasitical rotiferse to ex- 
pand (having frequently observed that these were more 
vivacious than the corallines which they infest), I was glad 
to find the Sertularia itself in a living state, the polypi 
speedily issuing from their cells, and enabling me to make 
some interesting observations. 
In this Sertularia several stems usually proceed from the 
same base ; these are filiform, jointed, and slightly waved, 
and support ail the branches and denticles in opposite pairs, 
and on the same plane. They maintain their primary rank 
throughout. 
The branches occur in pairs, rather remote, placed oppo- 
site to each other, and proceeding from the stem nearly at 
right angles. The joints on the stems occur immediately 
above the insertion of the branches. 
The denticles or cells are oval, sessile, and upwards of 
ten times the breadth of the stem. In general, they occur 
in pairs, at remote distances, on the stem or branches, pro- 
jecting nearly at right angles ; and are probably ultimately 
converted into branches, when no longer necessary as an 
integument to the polypi, as I have observed take place in 
the Sertularia gelatinosa of Pallas *. Sometimes they 
occur in the axillae of the branches, in pairs, or in greater 
numbers, crowded together. 
^he polypi, when expanded, project considerably beyond 
the mouth of the denticle, as at Plate XV. fig. 1., with 
* Edin. Phil, Journ. v. ii. p. 86. 
