334 



Birge — The Crustacea of the Plankton. 



single observations made since that date. In all cases the larvae 

 of all species of Copepoda were counted together; it being 

 practically impossible to assign them to their proper forms. 

 Unquestionably, however, the great majority of these animals, 

 belonged to Cyclops brevispinosus. All larvae beyond the nau- 

 plius stage were assigned to and counted with their proper 

 genera. 



Table XIV. — Nauplii, 



Average numbers, expressed in thousands per 

 square meter. 



1896. 



July 16-31 



August 1-15 



August 16-31 



September 1-15 



September 16-30 



October 1-15 



October 16-31... 

 November 1-15 . . 

 November 16-30. 

 December 1-15 . . 

 December 16-31. 



712.5 



477.8- 



350.8 



613.7 



606.6 



Maximum, July 18, 2,037,920. 



1897. 



January 11 . . . 

 January 21 . . . 

 February 17 . . 



March 3 



March 29 



April 8 



April 14 



Nauplii. 



Cyclops. 



1,550 



118 



1,284 



76 



513 



70 



722 



93 



714 



87 



726 



154 



798 



560 



April 17 

 April 28 

 May 4 . 

 May 10 . 

 May 15 . 

 May 21 . 

 June 6.. 



Nauplii. 



Cyclops. 



204 



390 



418 



619 



357 



1,121 



1,007 



921 



616 



774 



257 



1,767 



2,470 



1,169 



It is difficult to correlate the numbers of the nauplii with 

 those of the older and adult Crustacea. While Cyclops remained 

 numerous throughout the summer of 1896 there was no such rise 

 of numbers in late July and August as would be expected from 

 the great number of larvae which were present in the latter part 

 of July. The number of nauplii found in the early and middle 

 part of October is not as great as the increase in the number 

 of the Crustacea would have led us to expect. It is evident, 

 however, that the decrease of the Copepoda in the late fall and' 

 during the winter is due rather to the failure of the nauplii to 

 develop toward the adult form than to the absence of these 



