BRITISH MARINE POLYZOA. 83 
stomach with it, is a contractile cord, called the funtculus, which 
plays a very important part in the economy of the animal. This 
structure extends for a considerable distance along the walls of the 
stomach, and gives off filaments which reach to the endocyst. The 
funiculus expands a little at the base of the cell, and thread-like 
prolongations extend through the base through the pores of the 
diaphragms to the cell beneath, so forming a connecting link 
between the various portions of the Zoarzuwm or colony. The 
structure of the funiculus is uniform, and composed of cells very 
much resembling in shape the frustules of the diatoms /Vavicula. 
This funiculus is sometimes called the endosarc. Fritz Muller 
considered this endosarc as a colonial nervous system, and so des- 
cribed it, and his views were until recently very largely accepted. 
He considered it a great series of nerves serving not for the 
individual structures, but for the entire colony. Recently, how- 
ever, this structure has received considerable attention from 
Reichest, Joliet and others, who have very strongly opposed the 
nervous theory of Muller, and hold that the funiculus is a deriva- 
tive from the endocyst. This view is now generally adopted. The 
spermacyst is developed on the endosarc and the spermatozoa, 
and in many cases the ova proceed from it. The endosarc may, 
therefore, be looked upon as an extension of the endocyst, in 
which the cells are altered so as to form distinct shapes, and to 
have special functions specially connected with the reproduction 
of the animal and the union of the colony. 
In those polyzoa in which the orifice of the zocecium is pro- 
tected with an opercular covering, z.¢., in the Chezlostomata there are 
a number of curious appendages known as avicularia, or “ bird’s 
head” processes and wbracula. 
There are forty-five British genera of Cheilostomata in thirty-one 
of which are found avicularia, and in four of which vibracula are 
present. 
This bird’s head process differs in shape very much, varying 
from a slight differenticled zocecium to an elaborate structure like 
that of the Bugule. This structure is one which—viewed in 
any one species without consideration of others—would cause 
considerable difficulty in deciding its nature, but when the 
avicularia generally are considered it is found that a development 
of form can be clearly traced, which shows that the avicularia 
were originally slightly modified ordinary zocecia, and that through 
a multitude of phases they have passed in some species to highly 
specialized organs. In these avicularia are found an apparatus 
of muscles, and in most of them is found a cellular body, the 
analogue of the polypide. This polypide contains a nerve centre, 
and probably constitutes an organ of touch, as it is supplied with 
an apparatus of seée or bristles. The use of these appendages is 
