HARDWICKE'S SCIENCE-GOSSIP. 



269 



a contracting and expanding nature of that organ. 

 The lower part of the stomach at intervals is seen 

 to be contracted somewhat in the shape of an 

 hour-glass, in which for a moment part of the 

 contents of the stomach are retained, and then 

 again released to mix with the rest. After being 

 subjected to the action of the stomach for some 

 time, the alimentary matter is delivered by degrees 

 into the intestine {d), from whence it is expelled 

 •through the vent (o), in form of oval or egg-sliaped 

 pellets. 



great rapidity. No doubt this motion is produced 

 by vibratile cilia on the interior of the body, though 

 not to be observable. In some of the colonies of 

 the LopJiopus there are a number of globular bodies 

 {g), varying in size from the y^Wth of an inch in 

 diameter up to the size of an ordinary Volvox glo- 

 hator. These bodies are considered to be para- 

 sitical, as they do not appear to have any necessary 

 connection with the economy of the Polyzoa in 

 whose interior they occur. This would appear to 

 be the case from the fact that in some colonies not 



iTig. 177. Fresh-water Polyzoon {LnpTiojms erysfallina) : n, reg-ion of the mouth; /), oesophagus ; ^.stomach; d, intestine; 

 e, muscles ; /, statoblast ; g, parasitic globes ;/(,/(, mouth ; i, tentacles retracting: within cell ; k, outer transparent envelope ; 

 I, perigastric space ; m, lophophore; n, tentacles excised to show mouth ; 0, vent ; p, hollow globe ; r, place where division 

 commences ; «, cell. 



The perigastric space (0 is filled with a clear 

 fluid, which also extends up the lophophore (ra), in 

 which fluid are seen floating numerous particles of 

 very varied forms and sizes, the smallest ascending 

 to the tip of the lophophore {m). By the move- 

 ment of those bodies it is evident that there is a 

 constant rotating motion in this transparent fluid, 

 by which these particles are kept in a perpetual 

 whirl from one part to the other, and at times with 



one of them is to be seen, while in others they are 

 very numerous. 



In one instance of a colony under my observation 

 they were increased in such numbers of all sizes 

 that they entirely filled the perigastric space {I) 

 forcing the smaller particles up even into the lopho 

 phore {m), and ultimately bursting the whole 

 colony and escaping into the water, when all motion 

 n them ceased, and they soon disappeared alto- 



