ZOOPHYTES 381 



from the fleshy carpet, agreeing in every respect with those 

 which we have just examined, except that they are sessile, 

 instead of being carried by a polype. 



The fourth form is that of the tentacular polype. Here 

 and there, from amid the forest of shorter polypes ali- 

 mentary and reproductive white threads are seen pro- 

 truding, which extend to a length four or five times as 

 great as theirs, and hang down or loosely float in the 

 water. They are found on the outskirts of the whole 

 compound structure, and at each extremity of the long 

 diameter of the mouth of the supporting shell, so that 

 they must, in their natural condition, reach to the ground, 

 along which the crab -tenanted shell is carried, enabling the 

 Zoophyte to seize and appropriate the atoms scattered by 

 the crab whenever he takes his meals. The tips of these 

 organs are covered with a dense pavement of large thread- 

 cells; and they must doubtless perform the office of gen- 

 eral purveyors to the composite animal. 



But still more remarkable, more extraordinary than all 

 we have been considering, are the objects which are now 

 in view in the field of the microscope. You see a num- 

 ber of bodies, which Dr. Wright calls ophidian or spiral 

 polypes, and which, as he truly observes, are "like small 

 white snakes, closely coiled in one, two, or three spirals, 

 and grouped immediately round the mouth of the shell." 

 The habits of these polypes are still stranger than their 

 forms. "When touched, they only draw their folds more 

 closely together. But if any part of the polypary, how- 

 ever distant from them, be irritated, the spiral polypes 

 uncoil, extend, and lash themselves violently backward 

 and forward, and then quickly roll themselves up again; 

 and that not irregularly or independently of each other, 



