GERMAN PLANKTON INVESTIGATIONS. 307 



We now consider the right-hand portion of the form. 

 Under one heading the names of the species, the numbers 

 of which it is desired to estimate, are entered. To the 

 right of this are spaces in which the numbers of the glass 

 plates are entered. When the enumeration of a given 

 species is ended a query is placed in the column devoted 

 to the next plate. When no individuals are found a 

 cipher is naturally entered in the space provided. If, 

 on the contrary, a given species is being investigated, but 

 on certain plates not counted, a question mark is entered, 

 and the plates are not considered in the summation. In 

 the three last places on the right are entered the total 

 number of individuals counted, the number of plates used 

 in the enumeration, and thirdly the coefficient. Now, in 

 order to find the total number of individuals of a given 

 species in the catch, we have only to multiply the total 

 number counted by the coefficient, as above indicated for 

 Melosira. The number is then entered on the form in 

 the space provided for the purpose. 



The last heading to be considered is entitled " Under 

 one square metre." We have seen from what has been 

 written above in the description of the net that the whole 

 volume of water, calculated from the area of the mouth of 

 the net and the depth to which it is sunk, does not pass 

 through the net, but part of it passes over the edge. It 

 is therefore necessary to consider the filtration coefficient 

 of the net, that is, what number the volume or 

 number of organisms must be multiplied b}^ in order to 

 find the true value supposing the whole column of water 

 filtered through. In the present instance the coefficient 

 is 151*5, the estimation being made for one square metre 

 surface area of the water column. 



For Leptodora there are 9 females captured. In a 

 column of water of one square metre section and 20 metres 



