[currie] plankton COPEPODS 219 



segment of the forebody, which are rounded at the tip, each carrying 

 dorsally a conspicuous spinule. The terminal joint of p5 of the female 

 is much longer and slenderer than that of A. clausi, as it equals in 

 length the long plumose seta of the second joint. (Fig. 52). 



Rudimentary p5 in Pseudocalanus 



Pseudocalanus elongatus was the most abundant copepod taken 

 in the, tows during June, July and first part of August. The majority 

 of these were females with no fifth swimming legs, but on June 28th, 

 in a ten fathom haul taken at "Prince" Sta. 3, two females were noted 

 with rudimentary p5 (Fig. 53). This rare anomaly has been signal- 

 ized by A. Bœck (1864) and A. Mrazek (1902). Mrazek's figures are 

 reproduced by P. J. van Breemen in Nordishches Plankton, Bd. LV., 

 1908, p. 25. These rudimentary p5 are small, three-jointed appendages 

 with the terminal joint blunt, not tipped with a spinule. No females 

 of stage V were found with any trace of p5. All the males in stage V 

 have immature p5 which are four-jointed, tipped with a spinule, and 

 much larger than the rudimentary p5 of the adult female (Fig. 54). 

 The peculiar asymmetry of the p5 of the adult male is not evident in 

 Stage V, except that the left leg is slightly larger and longer than the 

 right. 



Immature p5 of Metridia 



Two species of Metridia occurred occasionally in the tows. 

 M. hicens and M. longa. Even in the immature copepodite stages, 

 not only the species, but the sex may be determined. From a vertical 

 haul made at "Prince" Sta. 3 on June 28, 1916, a number of Metridia 

 at different stages were obtained. There were three specimens of 

 M. lucens stage IV; one female and two males. Both female and 

 males were 1-4 mm. in length and had three joints in the p5. The 

 terminal joints of the p5 of the female are about equal in length to 

 each of the other joints and carry at their tips two slender setae (Fig. 

 55). 



The terminal joints of the male are two and a half times as long 

 as each of the other joints, and each carried three short external 

 setae, one terminal seta, and two internal setae (Fig. 56). 



There were seven specimens of M. lucens, stage V two females 

 and five males. One female was 2 • 1 mm. in length, the other measured 

 2 mm. and was exuviating to stage VI. Three of the males were 

 1 -9 mm. in length, the other two being 1 -8 mm., and 1 -3 mm. respec- 

 tively. The fifth swimming legs of the female were similar to those 

 of the adult except that one female had an outer seta on each of the 



