the spider-crab is able to reverse the current, so to 

 speak, the tube, it will be seen, only serves to 

 extend its course. 



Well, this reversion is exactly what takes place. 

 The spider-crab can alternate the stream, drawing 

 the water down the siphon thus formed to its gill- 

 chambers and discharging it at the rear. And this 

 discovery contained at once an answer to my sec- 

 ond question : A Hyas, when casting its molt, can- 

 not conceal itself in the sand or mud until its 

 antennae are sufficiently free to act as an incurrent 

 conveyor tube. 



In passing, I must also mention that the period 

 of this molting accords with those of other observa- 

 tions I have made ; these crabs, although not invari- 

 ably, usually molt during the night. 



II 



When, several days later, I next had oppor- 

 tunity to give my attention to Jim, he had so in- 

 creased in size that under his debris accumulated 

 on his back, I at first had difficulty in recognizing 

 him among his crab companions in the tank. The 

 crust he had discarded measured about four inches 

 including the legs when these were fully spread; 



[234] 



