384 
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... 
1113.8 
October 16-31. 
712.5* 
477.8 
350.8 
613.7 
606.6- 
August 1-15... 
529.7 
November 1-15. 
August 16-31. 
685.9 
November 16-30. 
September 1-15. 
310.9 
December 1-15. 
September 16-30. 
408.8 
December 16-31. 
October 1-15. 
200.4 
Maximum, July 18,2,037,920. 
1897. 
Nauplii. 
Cyclops. 
Nauplii. 
Cyclops. 
January 11. 
1,550 
118 
April 17. 
204 
390 
January 21. 
1,284 
76 
April 28. 
418 
619 
February 17.. 
513 
70 
May 4. 
357 
1,121 
March 3. 
722 
93 
May 10. 
1,007 
921 
March 29. 
714 
87 
May 15... 
616 
774 
April 8. 
726 
154 
May 21 ... 
257 
1,767 
April 14. 
798 
560 
June 6. 
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* 
