Harsh — The Planlion of Fresh Water Lahes, 185 



A few words in regard to the work on plankton which remains 

 for the future investigator. It will, I think, be evident, that so 

 far as exact and comprehensive knowledge is concerned, v\^e have 

 but entered a vast field. We know so little, that we can say 

 that we are just beginning to place limits on our ignorance. 



A svstematic knowled2;e of the fauna and fiora is a first and 

 fundaniental condition of comparative biological work. We 

 need accessible manuals by which the animals and plants dealt 

 with can be identified. Systematic work may not be the highest 

 or the most satisfying to the investigator, but it is very neces- 

 sary. The plankton student is met, at the very beginning of 

 his work, with a difficulty that is almost a complete block to 

 further progress ; although the number of forms with which he 

 has to deal in his plankton work may be very few, he has to have 

 the knowledge of a specialist in each group in order to identify 

 them. If a laboratory has a company of specialists, the material 

 is quickly identified by passing from one to another. But if the 

 investigator is by himself, he finds himself in a most discourag- 

 ing situation. The literature of the various groups is scattered 

 and fragmentary, and frequently is utterly useless to any one 

 but a specialist. There is need of a manual, or rather a series 

 of manuals, that shall so treat of the fresh water fauna and flora, 

 that any well-trained biologist shall have no difficulty in identi- 

 fying his material outside of the group which he may have made 

 his special study. 



It seems to me that we have nearlv reached the time when the 

 publication of such a manual should be possible. Most of the 

 preliminary vrork has been done. More, perhaps, remains to 

 be done on the botanical side than on the side of zoology, for the 

 exact study of the lower aquatic flora has been much neglected. 

 I hope that the time is not far distant vchen we may have such 

 a manual produced in this country, with the cooperation of our 

 best specialists. Nothing would do more to further the study of 

 plankton, for it would furnish the student with a tool of ines- 

 timable value. 



In reficard to the planlvton itself, verv little is reallv known 

 of the abvssal fauna and its controllins: conditions. I have 

 spoken of the fouling of the water at the periods of stagnation, 



