CGECOLOGY OF CIRRATULUS TENTACULATUS. 61 
When withdrawn from the mud Cirratulus presents an exceedingly limp 
and bedraggled appearance. The body appears to possess, when in this 
partially extended condition, absolutely no turgidity. This is in agree- 
ment with the animal’s marked thygmotactism, the necessary tension 
being secured in the natural habitat by the pressure of stones. 
A detailed account of the external characters is no longer necessary, 
owing to the recent appearance of Vol. 3 of Prof. McIntosh’s memoir on 
British Marine Annelids, containing the Cirratulide (1). It is sufficient to 
say that the species tentaculatus 1s distinguished by the occurrence of lateral 
filaments on segments anterior to the fifth chetigerous segment behind 
which the paired fascicles of filaments arise. 
Considerable doubt seems to exist as to the analogy of the lateral fila- 
ments with those of the paired tufts. Prof. McIntosh quotes Claparéde 
as distinguishing (in C. chrysoderma) between tentacles and branchiz in 
such forms by the fact that the former have only one blood-vessel, whilst 
the latter have two. In Audowinia filigera, on the contrary, every filament 
is branchial in structure. De St. Joseph (2) distinguishes between Cirra- 
tulus, in which the tentacles appear at the same time as the branchie, 
and Audouinia, in which the segments bearing the tentacles are preceded 
by a variable number of segments with lateral branchiz, and remarks that 
in neither case do the tentacular filaments and lateral branchie differ 
materially in external appearance. Cunningham and Ramage (3), on the 
other hand, describe a groove along the so-called tentacles and find it to 
contain only a single blood-vessel, whereas in the branchiz two blood- 
vessels are present. 
J. Bounhiol (4), in an ingenious paper on Respiration in Polycheetes, 
denies any respiratory function to either kind of filaments ; he says if a 
specimen of either Crrratulus cirratus or C. tentaculatus be placed in a glass 
vessel the floor of which is covered with sand, the animal is soon seen to 
make active use of the tentacular filaments to remove the sand grains, 
draw them towards itself and more or less cover itself with them. These 
filaments have been placed by anatomists in two categories, according to 
whether they contain a simple vascular caecum or a complete vascular 
circuit. The first are called tentacular filaments, the others gills. But the 
animal uses both kinds indiscriminately as prehensile organs. It has also 
been shown by experiment that the respiratory réle of these so-called gills 
is very feeble, and merely corresponds to an increase of the body surface. 
“La definition anatomique des branchies de Cirratulide n’est donc pas 
confirmée par l’expérimentation physiologique. Ce sont de simples 
organes prehensiles, tout comme les filaments prehensiles dont on avait 
cru pouvoir les distinguer.” 
The experiments of M. Bounhiol on Cirratulus in his examination of the 
