BIOLOGY OF THE ATLANTIC MACKEREL 



175 



That each scries includes truly homologous groups is indicated by several criteria, 

 independent of the straight-line conformity. In the R series, the modes all tend 

 toward peakedness. In the S series, they all tend to be broad. In the T series they 

 are intermediate in shape. The progress in each series is reasonably consistent and 

 the course of growth is roughly parallel in the three series; moreover, the slight depar- 

 ture from parallelism is in the expected direction, the later series having the higher 

 growth rates consistent with their development in the warmer water to which they 

 are subjected. Furthermore, the modes are consistently present in the material from 

 each cruise with only two exceptions, R in cruise III and S in cruise IV. The absence 

 of S in cruise IV is plainly due to failure on that cruise to visit certain stations in the 

 southerly end of the spawning area, where previous cruises woidd lead one to expect 



.6 



a 



1.0 



1.6 



1.2 1.4 



LOG OF LENGTH 



Fic.i'RE 6.— Frequency distribution of lengths of larvae plotted logarithmically. 



to find larvae of sizes appropriate for this series (fig. 13, IV). Absence of R in cruise 

 III has no such simple explanation, and can be explained only as chance sampling 

 fluctuation. 



Only one other reasonably sensible alternative to the series of homologies in figure 

 7 is possible. According to this alternative, R of cruises I and II would be considered 

 forerunners of the 9- and 10-mm. larvae of cruise III; S of cruise III considered the 

 forerunner of R of cruises V and VI; the 3- and 4-mm. larvae of cruise IV, the fore- 

 runner of S of cruise V; S of cruises V and VI, the forerunner of R of cruise VII; and 

 T of cruise VI, the forerunner of S of cruise VIII. But, this would not account for the 

 presence of such prominent modes as R of cruise IV, S of cruise VII, or T of cruise 

 VIII; and there are other objections to this alternative set of homologies which will 

 be considered later. 



