79 



that we are dealing in the case of the species of Dinobryon above 

 cited with a single variable organism, whose extremes of variation 

 only have been regarded as separate species. The connecting links 

 are sufficiently abundant still and the union of several types in a 

 single colony is sufficiently frequent to lend some weight to my con- 

 clusions with regard to those forms which have been under my 

 observation. In the interests of utility as well as in the interests 

 of well-grounded taxonomy, it is extremely desirable that the 

 establishment of new species among variable plankton organ- 

 isms should be attempted with extreme caution and only after the 

 fullest study of the range and conditions of variability. The insta- 

 bility of the taxonomic structures which Brunnthaler and Lemmer- 

 mann have recently raised, is evidenced by the differences in syno- 

 nymic, varietal, and specific rank given to the variants of Dino- 

 bryon by these two systematists, who have but recently mono- 

 graphed the group, largely if not wholly from the systematic point 

 of view. The changing estimate of validity which Lemmermann 

 himself has put upon his own species or varieties for example, 

 schauinslandii, pediforme, and curuatum rgives further evidence 

 that the basis upon which they rest is at the best but slight. 

 It is my firm conviction that the establishment of new species 

 among the organisms of the plankton of fresh water can be 

 satisfactorily accomplished only after careful analysis of the limits 

 of variation within the range of environmental conditions. Stand- 

 ards less comprehensive than this can yield results of but temporary 

 or local value and can lead to but little permanent advance in 

 science, and they bring only perplexity and chaos where order 

 should reign. 



Diplosiga frequentissima Zach.* Average number, 1,736,538. 

 This minute flagellate is found upon the rays of the colonial diatom 

 Asterionella, often in great numbers and so thickly set as to leave 

 little unoccupied space. It was found in each year at the time of 

 the vernal pulse of Asterionella in April-May, and was as a rule most 

 abundant immediately after the maximum growth of Asterionella 

 had been attained. Beyond an isolated occurrence in January it 

 was not recorded at other times than during the months of April 

 and May. 



Eudorina elegans Ehrbg. Average number, 14,362. About 

 twice as abundant in 1897. The distribution of this species is 



