ASTERIAS PALLIDA. 273 



(Fig. 2G />). At the anterior extremity of tiie bod y- cavity the.se two 

 «ort.s of fibres cross each other irreguhirly (Fig. 26 a). The presence 

 of these fibres alters tlie wliole aspect of the question whether the 

 ■current passing throngli the pore-canal is excnrrent or inciirrent. The 

 ■direction in Avhich the cilia are turned in killed specimens proves 

 nothing on this point ; but the presence of muscle fibres in the walls 

 ■of the body-caA'ity makes it possible for external water to pass in as well 

 as out. However, tlie effect of normal ciliary action I leave an open 

 question, having no observations of my own to offer on this point. 



The muscular fibrils above described not only persist, but are 

 more strongly develo])ed in the adult star where they are especially 

 nbtnidant on the aljoral side. 



'i'he epitiielium of the axial sinus presents a folding on the side 

 next the stomach, into which the surrounding tissue extends — the whole 

 formino- the well known ovoid ij-land. This oro-an extends throuofh 

 nearly the whole length of the axial sinus and is attached to its wall 

 a little to the left of the median line (Fig. 35). 



The wall of tlie hydrocœl ])resents nothing specially different 

 irom that of the enterocœl in the earlier stages of metamorphosis, except 

 that tlie five primary pouches have very tliick walls. AVhen the star is 

 complete and the ring-canal has been formed, the walls of the whole 

 hydrocd'l system are much thicker than those of the enterocœl, and 

 hence the two can easily be distinguislied in sections. The pore-canal 

 and the stone-canal have especially thickened walls. In Fig. o5 we see 

 the rudiment of the fold in tlie wall of the stone-canal, wdiich are to 

 become more complicated in the adult star. As the star grows the 

 difference just mentioned between the walls of tlie enterocœl and the 

 hydrocd'l becomes less and less pronounced, and in a star whose greater 

 radius is 5 mm. it has entirely disappeared (Fig. 34). In a star 

 whose radius is 2 mm. the musculature of the water-vascular S3^stem 



