INTRODUCTORY OBSERVATIONS. 7 



question, as in numerous other cases, performs the common functions of nutrition and 

 respiration. The rotatory movement observed in it appears to be due, as remarked by 

 Professor Allman, in part to the action of cilia with which the surface of the endoderm, 

 more especially of that lining the tentacular sheath, is furnished, and in part to the 

 varying contractions of the walls in the different and continual movements of the 

 animal. 



The chief bulk of the solid contents of the " cell" is formed by the alimentary canal 

 and its appendages. Commencing at the base of the lophophore, this canal descends 

 towards the lower part of the perivisceral space, and then turning abruptly upwards, 

 ascends to reach the upper part of the tentacular sheath, which it perforates nearly on a 

 level with the mouth. The alimentary tract admits of division in the usual way into an 

 oesophagus, stomach, and intestine ; to which, in some cases, may be superadded, a 

 dilatable pharynx and a proventriculus or gizzard, furnished with a masticatory apparatus. 

 The resophagus is contracted and muscular ; the stomach, which principally forms the 

 lower part of the loop, is much dilated, and in many cases partially divided into cardiac 

 and pyloric portions ; the intestine, which proceeds directly from the stomach to the anus, 

 is at first wide, but ultimately becomes much contracted. The whole tract appears to be 

 lined with vibratile cilia, and on the external surface of the stomach are placed numerous 

 brown hepatic granules. The mouth, at which the aliment enters, is placed, as already 

 observed, within a circle of tentacles, and it may be either a simple orbicular contractile 

 opening, or furnished with a peculiar, apparently protective organ, not unlike the epiglottis 

 in form, and termed by Professor Allman, the epistome. 



The nervous system of the Polyzoa is in a very rudimentary condition, being repre- 

 sented only by a small ganglion, usually of a yellowish colour, and placed as in the 

 Ascidians, on the dorsal or rectal aspect of the oesophagus, and thus between the mouth 

 and the anus. From it, in some few cases, fine nervous filaments have been seen to 

 proceed. 



The Polyzoa, so far as is known, are all hermaphrodite, 1 each individual being capable of 

 furnishing both the elements required for sexual reproduction. The organs destined for this 

 purpose are of the simplest kind, consisting of an ovary and testis. The ovary is a rounded, 

 sessile, or shortly pedunculate, granular mass attached to the parietes of the cell, near its 

 summit, in which the ova are developed by a gradual differentiation, and from which, when 

 mature, they escape by dehiscence into the perivisceral chamber. The testis is situated at 

 the bottom or lower part of the cell, usually in connexion with a long, cylindrical, granular 

 appendage, passing from the fundus of the stomach to the bottom of the cell, and which 

 has been termed by Professor Huxley, the " funiculus." From this testis the spermatozoa, 

 like the ova, escape into the perivisceral space in vast numbers, and there perform their 



1 With the exception, as it would seem, according to Professor Kolliker, of Alcyonidiurn gelatinosmn, 

 Johnst. (Halodactylus diaphanus, Farre). 



