2 Illinois Stale Laboratory of Natural History. 



quent page, already inaugurated and in successful operation. 

 It now devolves upon him to prepare for publication a de- 

 scription of this method, hut the credit for devising it and 

 putting it in operation belongs to those from whose hands he 

 received it. The apparatus was used without modification 

 until August 23, 1895, when the detachable bucket was 

 added to the net, and in October of the same year the separa-' 

 able carriage was introduced. In May, 1896, the pumping 

 method was substituted for the oblique haul in making plank- 

 ton collections. 



Upon the opening of the Station in April, 1894, the exam- 

 ination of the water by the plankton method was decided 

 upon, and in the early part of June the first regular collections 

 were made. The method of plankton collection ordinarily 

 employed, — as, for example, by Hensen ('87 and '95) in the 

 Baltic and North Seas and in the Atlantic Ocean, by Apstein 

 ('92 and '96) and Zacharias ('93-'96) in the lakes of northern 

 Germany, by Eeighard ('94) in Lake St. Clair, and by Ward 

 ('96a) in Lake Michigan, — has been without exception the ver- 

 tical haul, in which the net is lowered to the bottom of the 

 body of water and then raised in a vertical line to the surface, 

 thus filtering a vertical column of water. Difficulties beset 

 the application of this method to the waters at Havana. In 

 the first place all the bodies of water examined at the Station 

 are quite shallow, the majority of the plankton collections 

 being made in less than three meters of water. The river itself 

 is the deepest water in the locality, but at its lowest stage 

 there are only three meters of water in the main channel, 

 where collections are made. This depth is increased at times 

 of flood, the maximum reached in the past three years being 

 6.1 meters. The shallowness of the water thus practically 

 precludes examination by means of the vertical haul. 



A second difficulty exists in the unstable nature of the 

 bottom generally found throughout the locality to which the 

 operations of the Station are confined. This consists of a soft 

 black mud, composed largely of the detritus of decaying veg- 

 etation and alluvial soil deposited from the silt- charged waters 

 at times of flood. It is extremely unstable and upon the least 



