274 University of California PiiUications in Zoology [Vol. 18 



frequent on the surface when the temperature was ]8?4C or more, and 

 the aggregate forms as most abundant and most frequent on the sur- 

 face when the temperature was 18?3C or less. 



It is only by some such means of locomotion that I can conceive 

 how the observed differentials in abundance and great similarities 

 in frequency of the two generations could have arisen. Let it be 

 emphasized, however, that this is theory, not fact, and can be fully 

 established only by observations on moving protruding chains. But 

 if correct, verification ought not to prove difficult, for the theory 

 implies the same type of locomotion, though not the same type of 

 behavior relative to temperature, for every species within the genus 

 having similar double chains. 



2. Deduced Peculiarities in Temperature Relations 



If the foregoing theory of chain locomotion is correct, several con- 

 sequences in the distribution of the two generations are implied. It 

 is obvious that, were no solitary forms or aggregate forms ever 

 encountered except when attaclied together in chains, the frequency 

 of both generations would be identical with that of chains, and conse- 

 quently parallel to the abundance of chains. Whence, if long chains 

 accumulate on the surface in increasing numbers as the temperature 

 decreases, while sJiort chains accumulate in increasing numbers as the 

 temperature increases, chains, irrespective of length, would be most 

 abundant and frequent in the coldest and in the warmest water, and 

 least abundant and frequent in water of medium temperature. There- 

 fore, if as the theory stipulates, the frequency of each generation is 

 consequent upon the characteristic occurrence of protruding chains, 

 the frequency of both should not only be nearly identical, but should 

 decrease as the temperature increases from its lowest to its middle 

 values, i.e., from about 16?0C to about 18?5C, and then should 

 increase as the temperature increases from its middle to its highest 

 values, i.e., from about 18?5C to about 21?0C. Furthermore, on 

 account of the periodic segmentation of the stolon resulting, hypo- 

 thetically, in periodic breakage of the protruding chains at the ' ' inter- 

 mediate piece," it follows, as stated on page 273, that long chains 

 would be encountered more frequently than short chains. Hence, if 

 M represent the temperature half way between the two extremes, and 

 X any range in temperature, the frequency of both generations relative 

 to M — X should exceed that relative to M-^x. 



