46 ESTHER F. BYRNES. 



EXPLANATION OF PLATE II. 



Cyclops signatus var. tenuicornis. (Cyclops signalus var. annulicornis; C. albidus 



Jurine.) 



FIG. i. The inner ramus of the fourth swimming foot of an adult female, 

 showing the small distal seta on the inner margin of the distal segment. 



FlGS. 2 and 3. The fourth swimming feet of young C. tenuicornis in the sixth 

 stage of the metamorphosis. The ramus is unsegtnentcd. The antennae are 

 nine-jointed. 



FIGS. 4 and 5. The fourth swimming feet of a young C. tenuicornis (young of 

 Eig. i) in the seventh stage of the metamorphosis. The rami are two-jointed and 

 the antennae nine-jointed and few-jointed, respectively. 



FIG. 6. The fourth swimming foot of C. tenuicornis (young of Fig. i) in the 

 eighth stage of the metamorphosis when all the rami are three-jointed. The an- 

 tennae are twelve-jointed. 



All the young of Plate II. are sister forms from the same brood. Some are more 

 advanced in development than others, but they are all the same age. 



Two-jointed rami are usually correlated with ten-jointed antennae; three- 

 jointed rami are usually correlated with eleven-jointed antennae or with sevenleen- 

 jointed antennae as in the adult. 



