1918] Michael: Beliavior of Salpa democmtica 273 



formed in a very similar manner to those of S. democratica, Johnson 

 (1910, p. 151) says: "If one removes a large block from the chain, 

 the separation occurs at the first zooid of the block, leaving the entire 

 intermediate piece as the terminal remnant of the block that remains. ' ' 

 The intermediate piece, or salpa adjacent to it, is therefore a place 

 of weakness, or "deploying point" as Johnson (1910, p. 151) calls 

 it, and it seems likely that, if not accidently broken sooner, the strain 

 above mentioned will naturally break a chain of 8. democratica at this 

 point at about the time each block has been protruded into the water. 

 According to Agassiz (1866, p. 20), this separation must occur some 

 time before the entire block has been liberated, for, he says : ' ' These 

 chains escape through an opening formed at the proper time through 

 the tunic . . . which shows afterwards no trace of the passage. ..." 

 If this be true, the load carried by the solitary form will vary period- 

 ically as budding proceeds, from zero at one extreme to the condi- 

 tion where the combined locomotive power of the aggregate forms 

 greatly exceeds that of the solitary form at the other extreme. 



Moreover, if as seems likely, the number of protruding salpae 

 required to equal in locomotive power that of the attached solitary 

 form are few, compared to the number in the protruding portion of a 

 block at the time of separation, long chains would be encountered more 

 frequently than short chains. Again, is it not probable that the large 

 majority of hauls encountering a number of long chains would also 

 encounter at least one and in some instances many liberated blocks, 

 chain fragments, or detached aggregate salpae, while the large majority 

 encountering a number of short chains would also encounter at least 

 one and in some instances many solitary forms from which no salpae 

 protruded? If this question be ansM'ered in the affirmative, and if it 

 be granted that the preference, so to speak, of solitary forms to remain 

 on the surface increases as the temperature of the M^ater increases, 

 while that of aggregate forms increases as the temperature decreases, 

 it follows that long chains plus liberated blocks plus chain fragments 

 plus detached aggregate forms, would be most abundant and most 

 frequent in the coldei- surface water, while short chains plus detached 

 solitary forms would be most abundant but least frequent in the 

 warmer surface water. Finally, if each chain and liberated block and 

 chain fragment becomes broken up into its constituent salpae by the 

 swirl and pressure of the water during the process of towing (see 

 p. 260), it follows that the data, when tabulated as in the foregoing 

 tables, would reveal the solitary forms as most abundant and least 



