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nal pulse though there are slight traces of minor irregularities, and 

 on September 7, 1897, a single unusual deyelopment of 58,000,000. 

 Its optimum temperatures lie close to the maximum heat of summer 

 months. It is found not only in water-bloom and plankton, but 

 also along shores, on mud banks, and in sequestered pools and bays 

 where temperatures reach 90 and over. Lightly colored and semi- 

 transparent individuals of this and other species of the genus are 

 found frequently in the plankton, suggesting an approach to holo- 

 zoic nutrition in nature, such as Zumstein ('99) has demonstrated 

 experimentally in E. gracilis. Euglena is quantitatively one of the 

 most important links in the chain of food relations of the summer 

 plankton, converting nutrient matters in the water, both organic 

 and inorganic, into food for the Rotifer a and Entomostraca of that 

 season of the year. It in a measure replaces the diatoms, some of 

 which decrease in number or disappear during the warmer months. 



Glenodinium cinctwn Ehrbg.* Average number, 1,360,192. 

 This species is generally present from the middle of March till the 

 end of September, though sporadic occurrences are found in winter 

 months. There is a pulse on March 29 of 4,260,000 at a temperature 

 of 49, and another August 9 of 25,200,000 at 83. This small 

 planktont usually escapes through the silk net. It may be that 

 several species have been included, as the conditions of plankton 

 enumeration do not permit close scrutiny of such small organisms, 

 lacking prominent structural characteristics. It seems to be a 

 perennial planktont with a wide range of temperature adaptation, 

 and with a growing period approximating that of the land flora of 

 our latitude. 



Gonium pectorals O. F. Mull. This colonial flagellate has been 

 found in the water-bloom in large numbers, especially in the back- 

 waters. It was taken in the river plankton in 1897 and 1898 in 

 May and again in August and September. These pulses coincide in 

 location with those of Pandorvna and Eudonna. 



Lepocinclis ovum Ehrbg.* Average number, 401,538; silk 

 3,719. This species appears in the plankton in April and continues 

 until the end of October, with sporadic appearances in winter 

 months. There is no vernal pulse, and in both 1897 and 1898 maxi- 

 mum numbers, 43,200 and 50,400, occur at the height of midsummer 

 heat in August. In both years there are well-defined recurrent 

 pulses at intervals of three to six weeks to be traced in the silk 



