2 
CRETACEOUS CILTOPODA 
The anterior portion of the sac is revertil)le in itself ; its margin is supplied 
with a row of tentacles, in some of the fresh-water forms arranged on special, 
generally horse-shoe-shaped, thickenings, called the lophophor. These tentacles are 
externally provided Avith roAVS of Aubratile cilia, the chief function of which is 
probably to produce a current of AA'ater, directed towards the centre of the tentacles, 
hetAveen Avhich the mouth is situated. Whether the tentacles really act as branchiae 
is not fully ascertained. They are hollow, and the fluid Avhich fills the body is said 
to have been observed to pass up and downAvards in them. It yet, hoAvever, remains 
to be proved Avhether this is a true system of circiflation of the animal fluid or of 
the blood. No special blood, or vasculary- vessels exist, hut the fluid Avhich fills 
the body is kept in constant motion by the cilia lining the entne inner surface of 
the endocyst. I have on several occasions observed this current Avithin the body in 
some of the fresh-Avater Ciliopods, Avhich did not protrude their tentacles for several 
days, and from this fact I would he inclined to give the latter only a secondary im- 
portance in the system of respiration. It is not knoAvn in Avhat way Avater fin ds 
access to the internal body, Avhether through the mouth, or in consequence of the 
capillarity of the entire endo- and ecto-cyst, both of AA'hich are traversed by 
numerous canals ; certainly some such function must he attributed to the latter. 
The digestive organs consist of the mouth, the oesophagus and the alimentary 
canal, Avhich Avidens before the middle of its length into the stomach and then bends 
dorsally, gradually becoming thinner and terminating near the mouth at the outer 
or inner edge of the tentacular ring. Certain valves and appendages have been 
observed in the oesophagus of some of the marine Ciliopods, and in the fresh-Avater 
forms a valve also exists at the entrance of the stomach. The food has been seen 
to move up and doAvn in the stomach Avith the greatest rapidity before it entered the 
intestine, and the absorption of the nutriment appears to take jflace through both 
the stomachic and the intestinal membranes, through which it passes into the inner 
space of the body, and unites AAdth the fluid Avhich fills the latter. There are no 
special organs of manducation, and the only secretionary organ, which Avas ob- 
served in a few species, consists of a thin layer round a portion or the whole of 
the stomach, and is composed of cells filled AA'ith a yclloAA’ish-broAvn substance ; this 
organ appears to represent the liver, and has a situation similar to that in all the 
other classes of IMollusca. Besides the tentacles, which often act as prehensile 
organs, there are in the Chcilostomata group of the marine Ciliopods special organs 
serving apparently the same purpose ; these are the so-called A'ihracula and aA'icu- 
laria. The former are sinA])le long threads, often annulated; the latter resemble 
the head of a hu’d with the tAVO mandibles, and act prchensilely in exactly the 
same manner. Both generally secrete special tubes or small caAuties distinct from 
the ortlinary cells. 
The muscular system has a great number of longitudinal and transverse mus- 
cles ; the latter arc sometimes arranged in circular hands on the endocyst. Of other 
muscles the principal ones are those Avhich make the invagination of the anterior 
( 30 ) 
