CRABS AND SHRIMPS. 185 



shield, and, if long enough, is reflected over the front of 

 the shield between the eyes. The dorsal spine is bent 

 backwards and lies in contact with the dorsal shield ; for 

 the young, when it escapes from the egg, is quite soft, but 

 it rapidly hardens and solidifies by the deposition of cal- 

 careous matter in what may be called its skin. The pro- 

 gress of this solidification may be very beautifully observed 



SECOND STAGE OF SHORE-CRAB. 



(Megalopa.) 



by watching the circulation in the dorsal spine. When 

 the creature has just effected its liberation from the egg, 

 the blood-globules may be seen ascending to the apex ; 

 but as the consolidation advances, the circulation becomes 

 more and more limited in its extent, and is finally con- 

 fined to the base. These minute creatures, in this early 

 state of their existence, are natatory and wonderfully 

 active. They are continually swimming from one part of 

 the vessel to the other ; and, when observed free in their 



