226 MICROSCOPY FOR BEGINNERS. 



as on a base, usually in a double row. The word is 

 Greek, and means " wearing a crest." 



In those Polyzoa which secrete hardened, tubular, tree- 

 like sheaths on the surface of submerged objects, the 

 lophophore is protruded from the orifice in the end of 

 the branch much as in Pectinatella, and there is only 

 one animal to each limb and hollow twig. The protru- 

 sion and expansion of the lophophore can be seen with 

 a pocket-lens, as in Fig. 156 (from Professor Alpheus Hy- 

 att's work on the Polyzoa), when it resembles in form 

 that of Pectinatella. Those inhabiting the tubular 

 sheaths seem much more timid than the gelatinous 

 forms, retreating on slighter provocation, and remain- 

 ing longer before they reappear and again spread the 

 lophophore and tentacles. They are quite as graceful 

 and 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 Pec- 

 tinatella, or the eighteen to twenty in other members of 

 the group, are quite powerful, and setting in towards 

 the centre of the lophophore, they sweep the entrapped 

 food to the mouth. The body of the Polyzoon is a 

 transparent, membranous sack, with the lophophore and 

 the mouth at the free end, most of the rest being im- 

 mersed 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 



