1918J Michael: Behavior of Salpa democratica ' 257 



aggregate forms. For at least one individual of that generation might 

 be captured M^hich contained an embryo sufficiently mature to be 

 dislodged during the processes of towing and washing the net and 

 condensing and handling the hauls, and so be counted as a solitary 

 form. If such were the case, the frequency of solitary forms would 

 be identical with that of aggregate forms in colder water. But, even 

 so, this could not account for the fact that those solitary forms cap- 

 tured in the warmer water were accompanied by aggregate forms, for 

 the embryo does not carry the adult, and aggregate forms are shown 

 to be most abundant in cold water, while solitary forms are most 

 abundant in warm water. The second alternative, however, completely 

 satisfies the conditions, providing the chain of aggregate salpae remains 

 attached to the solitary salpa after being protruded from its mantle 

 cavity into the water. 



This will be rendered more intelligible, perhaps, if the problem 

 is stated in symbolical language. Let a solitary form be symbolized 

 by a cork, an aggregate form by an iron weight, warm water by the 

 surface of a pond, and cold water by the bottom of the pond. Flota- 

 tion is then analogous to accumulation in warm water, and sinking 

 to accumulation in cold water. Our problem may now be restated as 

 follows: Since corks float and iron weights sink, what is the relation 

 between them that necessitates taking some corks from the bottom of 

 the pond whenever a number of iron weights are taken therefrom, 

 and that necessitates taking some iron weights from the surface when- 

 ever a number of corks are taken therefrom? 



Stated in this symbolical language, it is evident that the only 

 feasible answer is that at the time the corks and iron weights were 

 removed from the pond, they were tied together. Now, if by experi- 

 ment, we find that one cork will barely float six weights, corks with 

 more than this number of weights attached would sink, while those 

 with less attached would float. Moreover, if those corks with more 

 than six weights attached usually outnumbered those with less 

 attached, while occasionally those with less attached far outnumbered 

 those with more attached, then both corks and weights would be so 

 distributed with respect to surface and bottom that, while corks in 

 the long run would be obtained in greater numbers from the surface 

 than from the bottom, at least one would be present in a larger per- 

 centage of bottom than of surface hauls. In other words corks would 

 be most abundant and least frequent on the surface, while iron weights 

 would be most abundant and most frequent on the bottom. 



