1923] 



Murphy: The Life Cycle of Oithona Nana 



451 



A second cycle was then started from reared adults. Two females, 

 B7 and B9, were transferred to a finger bowl with two males. E7 and 

 E13 (table 1). Eight days later one female was carrying egg masses. 

 Prom these, nine nauplii hatched, and two females and two males 

 reached maturity. The life cycle from adult to adult was completed 

 in ten weeks. 



III. STAGES OF DEVELOPMENT 



The eggs of Oithona nana are carried by the female in two sacs 

 until the nauplii hatch. The number of eggs to a mass ranges from 

 5 to 11. In experimental jars the nauplii appeared in 11 to IS days. 



Summary of Length op Stages and Body Length, 

 Oithona nana, Reared Specimens 



There are six naupliar, and five copepodid, stages before the 

 animal is fully formed. The complete number was recorded for 12 

 females and 9 males, as shown in table 1. 



Table 2 is a summary of the average length in days of each statre. 

 and of the average body length for each stage of the males and females 

 reared to maturity. 



Prom this table it is clear that the difference in size between male 

 and female is evident, as early as naupliar stage 3. The adult meas- 

 urements of the reared specimens are within the limits of the species 

 as stated by Giesbrecht (0.5-0.65 mm.; 0.48-0.57 m.), though some- 

 what smaller than those of specimens taken from the pier collections. 



The square-cut front of the head of the male (fig. 1) as opposed 

 to the bluntly rounded head of the female (fig. 2), is recognizable at 



