THE METAMORPHOSIS OF A CRAB. 207 



XXI. THE META3I0RPH0SIS OF A CRAB. 

 ( Callinectes hastatus. ) 



The material gathered at the surface of the ocean "with 

 the dip-net, as described in Section VII., will usually be 

 found to contain specimens of the various stages in the 

 metamorphosis of cralvlarvae. They are all sufficiently 

 alike to be used in verifying the following description ; so 

 it is not necessary to obtain the larvae of Callinectes. 



I. The Zoea Stage. If the water which has been col- 

 lected with a dip-net on a calm summer evening be placed 

 in a glass beaker and held before a light, numbers of crab- 

 zoeas will usually ])e found. They are very active, and 

 they show a slight tendency to collect at the surface on the 

 side nearest the light, although they may be found swim- 

 ming in all parts of the beaker. They may be recognized 

 by comparison with Fig. 105, which is a highly magnified 

 side view of the zoea of Callinectes about twelve hours 

 after its escape fi-om the egg. 



Catch several zoeas with a dipping-tube, and placing 

 them in a watch-crystal with a small quantity of sea- water, 

 examine them with a power of from fifty to one hundred 

 diameters, and notice : — 



a. The very large compound eyes (Figs. 105 and 

 106,^). * 



b. The shell, or carapace (Figs. 105 and 106, c), which 

 covers up the anterior portion of the body. 



c. The long, movable, jointed abdomen (a) which pro- 

 jects from underneath the posterior edge of the carapace, 

 and ends in a large, forked telson. 



d. Between the eyes the carapace is prolonged down- 

 wards to form a long, slender, pointed rostrum (Figs. 105 



