556 



INVERTEBRATA 



CHAP. 



figures are given by Carpenter (1866) of the stages described by this 

 author. The first stage described by him is the fixed larva with the 

 closed vestibule ; following on this he has seen the growth of the 

 arms of the young Crinoid. These arms arise as vertical upgrowths 

 of the calyx alternating with the oral valves. They are supported 



FIG. 411. View of the calyx of a tixed larva of Antedon rosacea from the upper side, in 

 order to show the adhesion of the lobe of the hydrocoele to the arm and the first 

 dichotomy of the arm. (After Perrier.) 



a, anus ; az.t, azygous tentacle formed from the tip of the primary lobe of the hydrocoele ; o, mouth ; 

 r.e, radial canal formed from the base of the primary lobe of the hydrocoele. 



each at its base by a new plate, the primary radial (R 1 , Fig. 410), and 

 as they grow in length secondary and tertiary radials are added 

 (R 2 , R 3 , Fig. 410). To these incipient arms the median tentacle in 

 each radius applies itself and becomes the radial canal of the arm 

 (r.c, Fig. 411). When the arm forks the tip of the radial canal 

 remains as an azygous tentacle at the fork, but two branches are 



