530 



COMPARATIVE ANATOMY 



CHAP. 



calcareous bodies form between this and the first pair ; these are the rudiments of a 

 second pair of ambulacral plates, and so on. 



FIG. 437. Asterina gibbosa, larva at the end 

 of the eighth day, from the left side (after 

 Ludwig). 1-5, The ambulacral rudiments of the 

 arms over the primary hydroccel bulgings ; I-V, the 

 antiambulacral rudiments of the arms. 



Fii;. 4:js.- Asterina gibbosa, larva ten 

 days old, seen from the left and some- 

 what from the ventral side (after Ludwig). 

 The ambulacral arm rudiments (1-5) now 

 have five lobes, ft, Terminal lobe, terminal 

 tentacle. 



As early as the seventh day, the rudiments of the apical skeletal plates, eleven 

 in number, appear. These eleven mdiments lie superficially below the ectoderm of 



PIG. 439. Asterina gibbosa, young 

 Asteroid, with much reduced lateral 

 organ (lo) at the end of the tenth day, 

 from the left side (after Ludwig). 

 The first rudiments of the ambulacral 

 skeleton have appeared (five pairs of 

 ambulacral plates). The mouth of 

 the Asteroid has not yet formed. 



FIG. 440. Asterina gibbosa, young Asteroid 

 eleven days old, horizontal section immediately 

 below the oral surface (after Ludwig). 1-5, The five 

 five-lobed outgrowths of the hydrocoel ring (aa) which 

 has not yet closed ; ax, the two outgrowths at the two 

 ends of the horse-shoe-shaped hydrocoel, which by 

 growing out towards one another and opening out 

 into one another close the hydrocoel ; lo, interradius of 

 the larval organ ; m, interradius of the madreporite. 



the apical region. Five of theni appear in the mesenchyme of the five apical brachial 

 rudiments, and become the terminals of the Asteroid arms, always remaining at the 



