METAMORPHOSIS OF CORYSTES CASSIVELAUNUS. 465 



least in tlie earlier stages^ are exclusively vegetable feeders. 

 7'lie Metazofea and Megalopa, on tlie other hand, have more 

 than once been found eating zoajas, and oven those of their 

 own kind, and I have fouud small pieces of worm or shrimp 

 muscle a very satisfactory food for the Megalopa. 



Development of the Larva. 



There appear to be four distinct stages in the development 

 of the larva preceding the Megalopa, but I am unable to 

 say how many moults are included in this period. The 

 zo?eas referred to the second stage differ among themselves 

 to a certain extent in the relative development of the parts 

 of the body, and this stage, consequently, is not very sharply 

 separated from those preceding and following it. 



First Stage (PI. 29, fig. 1). — The measurements of the 

 zosea at this period are as follows, the figures given being 

 the average of ten specimens. I have given here, as also 

 in the stages succeeding, the minimum and maximum for 

 each measurement. 



Averaj^e Minimum and maximum 



length. lenj^tlis. 



1. Length of rostrum 



2. „ dorsal spine 



3. Tip to tip of spines 



4. Length of body . 



5. „ thorax 



6. Ratio of 4 to 3, 1 : 1-66. 



The zoaea of Corystes is distinguished from all other 

 Brachyurous zoJBas hitherto described by the following 

 features : — The total length from tip to tip of the dorsal and 

 rostral spines greatly exceeds the total length of the body. 

 Li the majoiuty of zoaeas the two measurements are 

 approximately equal. The posterior edge of the carapace 

 bears a fringe of short settc. The forks of the telson have 



