up to select' the records of stage XI to 'be used in the analysis: (1) 

 At least four-fifths of the pilchard eggs of a given day's spa;vning must 

 have reached the stage, (2) there must be at least tv;o specimens of the 

 stage in each included record, and (3) there must be a reasonable cer- 

 tainty about the length of time of development, based on evidence of as- 

 sociated stages of development .li/ 



''iThon the length of time of development of each record of stage XI 

 meeting the criteria v/as plotted as the dependent variable against the 

 temperature of the \vater at the station of collection, a scatter of points 

 was obtained that apparently could be fitted best by a curved line. By 

 using the logaritlim of the time of development for plotting against the 

 temperature of the water a straight line distribution resulted (uppermost 

 curve in figure 1), which was subsequently fitted by the method of least 

 squares . 



A similar correlation of temperature v/ith length of time of develop- 

 ment was also made on three-earlier stages of pilchard eggs. III, VI, 

 VIII-IX (combined to give more items )£/ The fitted lines for these stages, 

 also shovm in figure 1, have about the same slope as the fitted line for 

 stage XI. In fact, Vi'hon tested statistically, the four lines were not 

 significantly different from each other (P>.05). The slopes are defined 

 by the b values in the equation Y = a+bX; these values are listed in 

 table 3 J together with other pertinent data concerning the correlations. 

 There is no evidence th-.t the relation between temperature and rate of 

 development changtid during incubation. Furthermore, the results obtained 

 for the four stages are so consistent that they justify confidence in 

 the reliability of the method of analysis. The time (in hours after spawn- 

 ing) to reach each of the four stages at teraperatiires between 13.5 and 

 17.0° C. is given by 0.5 degree intervals in table U. Within the tem- 

 perature range investigated, the time to reach a stage of development 

 is increased by about 7.15 percent for each 0.5° C. decrease in tempera- 

 ture. The total time of development to hatching, could be approximated 

 by adding two to three hours time to the values listed for stage XI at 

 the higher temperatures, and proportionately more as the temperature de- 

 creases. 



Although consistent results are obtained for the several stages, 

 there is a considerable spread of points about each line. The factors 

 causing this variability may be associated with either the tine of de- 

 velopment or v^ith the temperature. Variable elements associated with 

 time, undoubtedly account for most of the spread about the fovir fitted 



-' The records of stage XI meeting the above criteria are indicated in 

 table 6 by an asterisk. 



2' All records of these stages that could meet the three criteria pre- 

 viously described for stage XI v/ere used in the correlations; these 

 are indicated in table 6 by an asterisk. 



140 



