ASYMMETRY IN THE STARFISH. I 17 



Solaster, and Patiria (doubtless also in other species) to be rather 

 large and of some functional importance. It should also be noted 

 that (in Patiria) the asymmetry exhibited by this vesicle always 

 coincides with that exhibited by other coelomic structures. 



Development of Ilydropores and Pore-canals. On about the 

 fifth day the larva gives off, typically from the posterior end of the 

 left anterior ccelom, a dorsally directed hollow process, which 

 comes into contact with the larval body wall and breaks through 

 to form an open hydropore (Fig. 9). In Patiria the pore canal 

 and hydropore constitute a large and conspicuous landmark for 

 the determination of asymmetry. Without a single observed 

 exception the hydropore is formed on the same side as the already 

 formed posterior ccelom. There were a few cases in which the 

 posterior ccelom appeared to be median, while the hydropore 

 appeared only on one side. Attention should be called here to 

 the fact that, while in Poranus (Gemmill, '15) the hydropore 

 appears a day or so earlier than the posterior ccelom, exactly the 

 opposite time relation prevails in Patiria, the posterior ccelom 

 appearing a day or so earlier than the hydropore. Probably the 

 earlier appearance of the posterior ccelom in Patiria accounts for 

 its larger size and its permanency. 



As was the case with the posterior ccelom, the hydropore also 

 shows reversed asymmetry. The reversed or right-handed larvae 

 are as large, as vigorous, and as healthy as are the more typical 

 individuals. A census of 652 individuals, belonging to seven 

 different lots of larvae, showed 589 with left-hand hydropores, 63 

 with right-hand hydropores, and none with both right-hand and 

 left-hand hydropores; which means that over 90 per cent, are 

 left-handed, and less than 10 per cent, are right-handed. We see 

 then that the percentage of individuals with completed right 

 hydropore is somewhat less than that of individuals with right 

 posterior ccelom, but the difference is not significant, as both are 

 very close to 10 per cent. Furthermore it may be said that the 

 above censuses were made upon different lots of larvae from those 

 given for controls in the experimental part of the paper, and 

 strongly tend to confirm the latter. 



It should strongly be emphasized in this connection that the 



right-hand hydropores in Patiria are not merely temporary 

 8 



