242 AQUATIC MICROSCOPY FOR BEGINNERS. 



the tubular sheaths seem much more timid than those 

 in the gelatinous forms, retreating on slighter provo- 

 cation, and remaining longer before they reappear and 

 again spread the lophophore and the tentacles. They 

 are as graceful and as attractive — perhaps they are 

 more so, since they seem more delicate and less able 

 to protect themselves. 



The tentacles are finely ciliated, as the microscope 

 will show. The currents produced by the active vibra- 

 tions of the cilia on the sixty to eighty tentacles of 

 Pectinatella, or the eighteen to twenty in other mem- 

 bers of the group, are powerful, and setting in towards 

 the center of the lophophore, they sweep the entrapped 

 food to the mouth. 



The body of the Polyzoon is a transparent, mem- 

 branous sack, with the lophophore and the mouth at 

 the free end, most of the rest being immersed in the 

 jelly, or concealed in the brown opaque sheath. The 

 mouth has on one border a short tongue-like organ, 

 which can close the opening and prevent the escape of 

 the food, and extending from the mouth to the stom- 

 ach, is the food-passage or oesophagus. The stomach 

 itself is a widened tube, usually conspicuous on ac- 

 count of. its contents and the alternate narrow, reddish- 

 brown and yellow bands traversing it lengthwise. It 

 is suspended in the hollow body, and is bathed by a 

 colorless fluid which fills the body-cavity and extends 

 also into the hollow tentacles. The stomach is fol- 

 lowed by the tubular intestine, which curves forward, 

 and generally opens below and on the outside of the 

 lophophore. The animals have no heart and no blood, 

 unless the liquid in the space between the outer walls 

 of the stomach and the inner walls of the body can be 

 said to be blood. 



