388 



SCIENCE, 



[N. S. Vol. XI. No. 272. 



thorough study of the fauna and flora of 

 Lake Tanganyika and the other lakes of 

 Central Africa. So far as explorations have 

 gone this ' halolimnic ' fauna as it has been 

 named, is peculiar to Lake Tanganyika, but 

 we may expect to find more or less of it in 

 other lakes. 



A few words in regard to the work on 

 plankton which remains for the future in- 

 vestigator. It will, I think, be evident, 

 that so far as exact and comprehensive 

 knowledge is concerned, we have but en- 

 tered a vast field. We know so little, that 

 we can say that we are just beginning to 

 place limits on our ignorance. 



A systematic knowledge of the fauna and 

 flora is a first and fundamental 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 necessary. The plankton student 

 is met, at the very beginning of his work, 

 with a difi&culty 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 dis- 

 couraging situation. The literature of the 

 various groups is scattered and fragmen- 

 tary, 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 identifying his 

 material outside the group which he may 

 have made his special study. 



It seems to me that we have nearly 

 reached the time when the publication of 



such a manual should be possible. Most 

 of the preliminary work 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 when 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 inesti- 

 mable value. 



In regard to the plankton itself, very 

 little is really known of the abyssal fauna 

 and its controlling conditions. I have 

 spoken of the fouling of the water at the 

 periods of stagnation, but our knowledge 

 of the conditions of the water at those 

 times is very imperfect. There should be 

 a systematic examination, by chemical an- 

 alysis of the water and its contained gases, 

 and of the mud of the bottom, and an ex- 

 act comparison should be made between 

 the lakes with sterile bottom waters and 

 those with a comparatively abundant fauna. 

 In connection with this should be a study 

 of the currents of the abyssal region. A 

 more careful and thorough examination 

 should be made of those lakes whose geo- 

 logical history indicates that they were 

 formerly connected with the sea, and may 

 contain a ' fauna relicta. ' I may say that 

 it is not likely that such explorations will 

 yield any startling results. The time for 

 that is probably past, and the lake student 

 of the future must content himself with 

 hard work, without the satisfaction of bril- 

 liant discoveries. 



Our quantitative knowledge of plankton 

 is only a beginning. We know something 

 of the conditions on a few lakes, but only 

 on a few, and we do not know what varia- 

 tions may be caused by the peculiarities of 

 individual lakes. Even in the same lake 

 the conditions may change from year to 



