THE DEVELOPMENT OF RHINCALANUS 



213 



and a posterior region in which three additional somites can be seen under the skin just 

 before the moult. 



Stage VI. Length: R. nasutus, 1-16 mm. ; 

 R. cormitus, 1-33 mm. 



I have seen only one specimen of R. nasutus 

 at this stage, which is probably below the 

 average length. 



Antennule with setae 9-A-6. 



Maxillule and maxilla projecting as small 

 lobes, the former with a few slender setae, 

 and the latter with two small spines. Maxilli- 

 pede represented by a small fold bearing 

 a spine and a seta, and borne upon the same 

 somite as the rudiment of leg 1 . Legs 1 and 



2 both represented by bilobed rudiments 

 bearing small spines. The general form of 

 the copepodid appendages can generally be 

 traced under the skin, the rudiment of leg 



3 being distinctly visible. 



COPEPODID 



St ageI, R. cormitus. Length i^i-i-jmm. 



This stage differs from later stages in 

 having the head scarcely produced, and 

 without rostral processes. The somite of 

 leg 4 is separated, with a pair of dorsal 

 spines, and the somite of leg 5 can be seen 

 under the skin of the terminal somite. The 

 furcal rami are not separated from the somite, 

 and bear five setae. Of the three terminal 

 setae one is inserted rather dorsally and is 

 soft, presumably corresponding to the soft 

 seta of the nauplius, and the inner seta of 

 the left side, which is much the longest in 

 later stages and in the adult, is of the same 

 length as its fellow of the right side. It is a remarkable fact that it is the right spine 

 which is longest in the nauplius. 



Fig. 7. Rhincalanus cormitus. Copepodid, stage I. 

 A, lateral view; B, furcal rami, dorsal view. 



