A Visit to Llandudno. 15 



out of doors, while the lighter mass below it, still under process 

 of digestion, performed the circumtwistatory movement im- 

 parted to a leg of mutton by a roasting-jack. In some other 

 Polyzoa, as the Plumatella, the food is tossed backwards and 

 forwards up and down the digestive tube. 



In the sketch some of the stalks are without heads, or more 

 properly bodies, and on this subject Johnston observes* that, 

 " like the hydroid Tubularin83, the life of the body is of shorter 

 duration than that of the stalks, the former fading or falling 

 off, when a new one is reproduced in its place." He likewise 

 cites Professor Eeid to the following effect: — "A few days 

 before this (the falling off of the body) takes place, the tenta- 

 cula are permanently bent inwards, and the membrane sur- 

 rounding their lower parts remains contracted, so as to com- 

 pletely, or nearly completely, cover the upper surface of the 

 body, presenting, in fact, the appearance which the animal 

 temporarily assumes when disturbed. The body then becomes 

 more opaque, and at last falls off. When this has taken place 

 the stalk retains its property of alternately contracting and 

 relaxing its different surfaces at intervals, upon which its move- 

 ments depend. After the lapse of a few days the top of the 

 stalk enlarges, and a minute head presents itself, in which the 

 different parts of the body are developed." This is an interest- 

 ing fact when it is considered that the body contains the mouth, 

 stomach, and other important organs, and also the nervous 

 ganglion which performs the functions of a restricted brain. It 

 is an instance of the power of the colonial life which animates 

 every member of a polyzoan group in addition to what we may 

 term his individual life, and is evidently a process of the same 

 character as that which forms the original offshoots from the 

 parent stem. Inside the mouth cavity, and below the tentacles, 

 ciliary action may be observed, and favourable specimens dis- 

 play the circular band of muscles running round the margin of 

 the cup, whose function is to pull it together. 



Professor Allman discovered an arrangement of the tenta- 

 cular disk which approaches these creatures to the Hippocrepian 

 Polyzoa, that is to those in which the tentacles are arranged 

 not in a circular, but in a horse-shoe group. Three species 

 may be found on our coasts : the P. echinata, just described, 

 with spines on its stalks; the P. gracilis, which has stalks 

 smooth, thin, and long • and the P. Belgica, with smooth stalks 

 inflated about the middle. The stalks rise from a creeping* 

 shoot, and the creatures are commonly found parasitic on 

 corallines and sea-weeds, between tide marks, but especially 

 near low-water mark. The species mentioned above vary in 



* A History of British Zoophytes, by George Johnston, M.D., LL.D. Second 

 edition, p. 384. 



