30 



MAUVELS OF POND>LIFE. 



there is no distinction of organs or parts. In the 

 next phice this tube has tivo orifices^ one for re- 

 ception, another for excretion ; while in animals like 

 the Polyp, (to be described in our next chapter,) 

 the digestive cavity has only one way in and out. 

 The bells or cups are not, as might be fancied 

 from a casual inspection, open like wine-glasses at 

 the top, but furnished Avith a retractile disk or cover, 



YorticcUa microstoma, shewing- allmeJi- Vorticella microstomo, the oncysted 



tary tiibe, ciliated mouth, and formiitiun animal piotrudin? through a supposed 

 ot ii yemma at the base, 300 linear. — 67c/». rupture ot the tunic. 



on which the cilia are arranged. Their stalks are 

 not simple stems, but are hollow tubes, which in 

 tlie genus Vorticella are furnished with a muscidar 

 band, by whose agency the movements are principally 

 made. 



Some of the Vorticellids will be observed to leave 

 their stalks, having developed cilia round their base, 

 and may be seen to swim al)out in the enjoyment of 



