50, 



fig-aro 53. This groove deepens, apparently by the groTTtl-i of tlio 

 parts on each, side, figure 54, and gives rise to a "sole" resembl- 

 ing that of the adult, figures 2, and 9, The novenents of the 

 foot no^'T closely reseiible those of the adtilt, but locomotion is 

 still materially aided by the poTT'erf'j.l cilia along its sides. 



The formation of the "sole" is accompanied by the growth 

 of the poster© -ventral portion of the foot into a more and more 

 prominent portion resembling a heel. The use of this outgrovrbh 

 is not evident. It remains in the adalt as a small projection, 

 just behind the opening of the jbyssal gland ; an organ that makes 

 its appearance about a day after the test is cast, but does not 

 seem to secrete threads. 



About the tim.e that the test is cast away, a thickening 

 makes its appearance on the inside of each mantle lobe, near its 

 posterior border, figures 34 and 35 g. • 



This thickening, the rudiment of the gill, accjuires 

 cilia and grows anteriorly so as to project over the mantloi-sur- 

 face. A constriction appears near the middle of each gill, 

 figure 36, g, deepens, and divides it into almost equal lobes. 

 Beneath its epitlieliiim, following the curve of its antei-ior ra8.r- 



« 



gin, is a chit*nous bar, the two ends of //hich lie near the ends 

 of the lobes, figure 36, cr. 



