378 EVENINGS AT THE MICROSCOPE 



We restore the strange partnership shell, fleece, and 

 crab to the glass of sea- water; j^rhere we soon see the 

 whole tumbling about the bottom in uncouth agility. As- 

 sist your eye with this pocket lens, and look again. The 

 shaggy nap upon the shell now bristles with tall slender 

 polypes, crowded and erect, like ears of corn in a field. 



No high power of magnification is necessary to furnish 

 us with considerable entertainment from this populous col- 

 ony. The polypes stand individually nearly half an inch 

 in height; each consists of a straight slender column, sur- 

 mounted by eight straight rod-like tentacles, four of which 

 stand erect, slightly diverging, and the other four, alter- 

 nating with these at their origin, extend horizontally like 

 the arms of a turnstile. 



The rough jolting of the crab over the stones the ex- 

 panded polypes bear with equanimity; they are used to 

 it; and though their tentacles wave and stream hither and 

 thither, they are not retracted on this account. But just 

 touch with the point of the pencil in your hand any part 

 of the shaggy fleece, and instantly the whole colony retire 

 together, as if by a common impulse, apparently shrinking 

 into the substance of the shell. Yet they soon reappear, 

 one after another quickly protruding its closed tentacles, 

 which are presently expanded as before. 



The explanation of this phenomena is, that the whole 

 colony of polypes are but the free points or feeding 

 mouths of a common living film, which invests the shell; 

 just as in Laomedea the polypes that inhabit the vase-like 

 cells are the off-shoots or free points of the common 

 medulla. 



The investing film will sometimes in captivity spread 

 upon the glass side of a tank, and then develop all the 



