71 



striking instance of marked inequalities in distribution within 

 small areas, of at least one plankton organism. 



Carteria showed great variation in the amount of chlorophyll 

 present. Some individuals were practically colorless. It seems 

 very probable that in the presence of great abundance^ partially 

 decayed organic matter such as occurs in a sewage-laden stream, 

 Carteria may become largely holozoic in its nutrition, as Zumstein 

 ('99) has shown to be the case with Euglena. The literature of 

 fresh-water plankton contains no record of a similar preponderance 

 of Carteria in other localities, though its occurrence has been occa- 

 sionally noted in the plankton. 



The chemical conditions under which this great pulse of Carteria 

 appeared in the autumn of 1897 can be followed in Part I., Plate 

 XL IV and Table X. The high chlorine and the great increase in free 

 ammonia and nitrites indicate the decay of sewage; the high 

 nitrates and albuminoid ammonia show that there was no lack of 

 some at least of the important sources of food. The two principal 

 pulses appear September 7 (2,846,250,000) and October 5 (6,476,- 

 400,000), with a minimum of 680,400,000, on September 21, sep- 

 arating them. Both of these pulses are attended by sharp declines 

 in nitrates and nitrites and free ammonia, and very slight decreases 

 in organic nitrogen and albuminoid ammonia. Either the first 

 three substances named or those matters which supply them by 

 their decay, are thus noticeably utilized at the times of these pulses. 



The relation of the Carteria to the volumetric pulses is (Pt. I., 

 PI. XI.) not a constant one. The Carteria pulse of September 7 

 lies in a slight depression between two maxima of the volumetric 

 curve, and a week prior to the autumnal culmination on September 

 14 at 19.8 cm. 3 per m. 3 . It thus appears during the growth period 

 of this volumetric maximum. The second and larger pulse of 

 Carteria, on October 5, coincides with the second volumetric maxi- 

 mum, and in fact fluctuates throughout with it. Though Carteria 

 constitutes but a small part of the actual catch of the silk net, 

 owing to leakage through the silk, it is apparently an important 

 factor in the food cycle which builds up such maxima. 



Ceratium brevicorne Hempel. This species appeared in small 

 numbers in isolated instances from April through October. It 

 varies towards C. hirundinella, but the small numbers in which it 

 has occurred have not as yet afforded sufficient ground for regard- 



