THE POLYZOA. 25 



Tho mouth (Fig. 8) leads into a long and wide pharyngeal 

 and oesophageal tube, which opens, below, into a definite stomach. 

 From this is continued a distinct intestine, which bends upon 



Fig. 7. 



Fig. 7. — Plumatella repens, a freshwater Polyzoon, magnified (after Allman). 



itself towards the oral end of the body, so as to form a sharp 

 angle, and then terminates upon the outer surface near the 

 mouth ; so that we have here, for the first time in our ascend- 

 ing survey of the Animal Kingdom, an animal possessing a 

 complete intestine, not only structurally separated from the 

 general substance of the body, and provided with permanent 

 apertures, as in the Hydrozoa and Actinozoa, but completely 

 shut off from the perivisceral cavity, and in direct communica- 

 tion only with the external medium. All the Polyzoa possess 

 a nervous system, the characters and position of which are 

 very well defined. It consists of a single ganglion (Fig. 8, w), 

 placed between the oral and the anal apertures, and sending- 

 off nerves in various directions. It has been affirmed that, 

 in some Polyzoa, there is a more extended system of nerves by 

 which the various zooids of the compound organism are placed 

 in communication ; but of that we want further evidence. In 

 these animals no heart has been discovered as yet, the matters 

 which result from digestion percolating through the walls of the 

 intestine, and becoming mixed with the perivisceral fluid. One 

 of the structural characters which I have mentioned is exceed- 

 ingly important. As I have said, the intestine is not straight, 



