86 Dr Fleming on the Natural History 
and again return to be ejected. The fluid thus circulating, did 
not seem to move in a solid body through tubular vessels, but 
to be divided into minute globules, which permeated a cellular 
structure. 
In general, there are several principal stems adhering to the 
same stone, and a few younger ones springing up at their base. 
In the situation in which I have observed them, they are never 
permitted to outlive the winter, being cut ofl* during that season 
by the drifted ice. They appear to be very common in the 
Tay above Balmerino, towards Flisk beach. It is at this latter 
place only where I have observed them in situ. Here the 
water is brackish, and its other conditions, as influenced by the 
tide, have been detailed in my paper on the ‘‘ Junction of the 
fresh water of rivers with the salt water of the sea,” in the Trans, 
of the Royal Soc. of Edin. vol. viii. p. 507,-513. 
This species is vivacious, the polypes bearing to be kept out 
of the water for more than a day without perishing. It is in- 
deed a littoral species, living in places left dry every tide. When 
kept in water, without being changed, the polypes soon contract 
within the denticles, and tlie body of the polype ceases to be 
visible in the stems. In some specimens, which I had neglect^ 
ed for upwards of a fortnight, the water not having been re- 
newed during that time, I found all the polypes in the denticles 
shrivelled up, and numerous white threads projecting from the 
branches. Upon examining the origin of these threads, I found 
that some of them proceeded from the base of the stems, but in 
general they were formed from an elongation of the foot-stalk of 
the denticle, its cup having disappea,red. The filaments con- 
sisted, as in the stalks from which they proceeded, of a soft co- 
vering, and a contained medullary cord. The extremities of these 
filaments were club-shaped ; and soon assuming the form of a 
denticle, gave opening to the tentacula of a polype which had 
been formed within. The base of this new denticle was annu- 
lated, as in the older ones. 
In the same pools with this Sertularia, may be observed the 
Tubularia ramosa, and a Flustra which does not appear to have 
been described. The latter I first found in 1806 on Leith shore. 
It differs from all the other British parasitical species, as pilosa, 
dentata^ lineata and membranacea. The F. bullata of So- 
Jander and from him copied by Stewart and Turton, is mere? 
