ANNELIDA. 



annexed figure represents the 

 curious habitation of the Te- 

 rebella Medusa, constructed 

 by cementing together minute 

 shells and other small bo- 

 dies. In neither case is there 

 any muscular connection be- 

 tween the worm and its abode, 

 so that the creature can be 

 readily drawn out from its 

 residence in order to ex- 

 amine the external appen- 

 dages belonging to the indi- 

 vidual segments of its body. 

 When thus displayed (fig- 

 97), the modifications con- 

 spicuous in the structure of 

 the lateral oars are at once 

 seen to be in relation with 

 their circumscribed move- 

 ments, and offer a wide con- 

 trast to the largely developed 

 spines, setse, and tentacular 

 cirri, met with in the Dorsi- 

 branchiata. In the upper 

 part of the body, rudimentary 

 protractile bunches of hairs 

 are still discernible, but so 

 feebly developed that their 

 use must evidently be restrict- 

 ed to the performance of those 

 motions by which the protru- 

 sion of the head is effected ; 

 while upon the posterior seg- 

 ments even these are oblite- 

 rated, the only organs at- 

 tached to the rings being 

 minute foot -like processes 

 adapted to the same office. 

 The tentacular cirri, which 

 were likewise distributed 



F/2-. 96. 



