Îcurrie] 



PLANKTON COPEPODS 



211 



with both large and small teeth together (Figs. 13, 14, 15) suggesting 

 that new teeth may be intercalated. This idea was strengthened 

 by the observation that the nuclei below the small teeth were usually 

 very large and closely appressed to the cuticle, as if indicating active 

 metabolism. One specimen occurred with supernumerary teeth 

 (Fig. 7), five needle-shaped teeth at the proximal end of the left basal 

 joint, while the other teeth on this joint were large and numerous. 

 Another specimen with a normal row of ten teeth on the left B I was 

 abnormal in having but one tooth on the right B I but had a normal 

 internal row of the teeth of stage V. This is not only a proof that the 

 few-teeth-small-size-class exuviates directly to stage V, but that an 

 abnormality occurring in one stage may disappear in the next. The 

 large size class may have large teeth (Figs. 16, 18, 19) or small teeth 

 (Fig. 17). As a rule, in this class, the teeth are large and crowded 

 in an irregular marginal row. 



These two quite distinct tooth classes seemed to indicate that 

 there is an ecdysis during stage IV. It would be expected, if this were 

 true, that the numbers of individuals belonging to each class would be 

 about equal. This is not the case as mentioned before and illustrated 

 by the graphs. 



Exuviation. The most convincing proof of ecdysis during stage 

 IV would be to find a copepod of the few-teeth-small-size class 

 exuviating to the many-teeth-large-size-class. Instead of this, 

 it was found that the copepods of both classes exuviate directly to 

 stage V, as shown in the following table, in which the features peculiar 

 to stage V of each individual were easily recognized through the 

 exuvia i.e., internal teeth, segmentation and number of setœ (Fig. 

 20,22). 



Table I. 

 Copepods of Stage IV in Exuviation to Stage V. 



