328 bulletin: museum of comparative zoology. 



le with the deep ones, because they were made with small 



nets. 



Thus the volumes of plankton per cubic meter, as calculated from 

 the quantitative hauls, would be more representative of the true condi- 

 tions, if the depths below about 40-50 fathoms were left out of account, 

 because it appears that the vertical net can have caught but little 

 below that level. In other words, to assume that the volume of plank- 

 ton taken at, say, Stations 10092 or 10093, was evenly distributed down 

 to 100 fathoms or more, results in far too small a density per cubic 

 meter for the upper layers of water. I have attempted to offset 

 this error by another table in which the volume of plankton per cubic 

 meter is calculated on the assumption that the whole catch was made 

 in the upper fifty fathoms. But this, though a closer reflection of 

 actual conditions, is unsatisfactory, because the plankton is not 

 vertically uniform even above fifty fathoms. Volume is itself so 

 rough a measure, that it has largely been abandoned by students of 

 plankton. But no other classification so far proposed gives so satis- 

 factory an index of the comparative density of the plankton as a 

 whole, as distinguished from its various individual components. 



According to this table, the plankton was densest off Massachusetts 

 Bay (Station 10087) and off Mt. Desert Rock (Station 10100); dis- 

 tinctly less so over the central parts of the Gulf and the off shore waters 

 in general. It was scantiest near the coast off Mt. Desert, and north- 

 east of Cape Ann (Station 10105). And the plankton was rather less 

 dense all along the coast, north of Cape Ann, than further off shore. 



The table of qualitative hauls (p. 326) might suggest a rather differ- 

 ent distribution, with the plankton densest in the centre of the Gulf 

 (Station 10090) and off the mouth of Penobscot Bay (Station 10091): 

 but this is not a valid objection to accepting the results of the quanti- 

 tative hauls as approximately correct, because, with the plankton 

 stratified as it undoubtedly was (p. 290), it was a matter of chance 

 whether a horizontal net hit or missed the richest zone. 



