SEA-FISHERTES LABORATORY. 355 



and how the catching power of a new net diminished from 

 day to day. We figure here photographs, which have been 

 kindly taken for us through the microscope by 

 Mr. Edwin Thompson, of (fig. 20) the silk of a new net 

 before being used, and (fig. 21) with the same magnifica- 

 tion a piece of silk from an old net that had been used for 

 some months. The flattened and swollen condition of the 

 fibres, the distortion and reduction in size of the meshes, 

 and the absolute closing up of some of them is obvious, 

 and accounts clearly for the reduced straining power of 

 the net. 



CONCLUSIONS. 



In the two preceding parts of this Report we have 

 drawn certain conclusions, some of which may now be 

 re-stated, and revised where necessary, in the light of the 

 third year's work. 



Total Plankton.— The most remarkable feature of 

 the distribution of the total plankton throughout the year 

 is the great increase in spring, due mainly to the sudden 

 appearance of enormous quantities of Diatoms. This year 

 the vernal maximum was later than in the two previous 

 years. It extended from April far into May, and died off 

 suddenly between the 24th and the 28th of May. 



There is usually a second less marked and less 

 constant increase in the plankton in September-October. 

 It is largely composed of Copepoda, although some 

 Diatoms, and on occasions Dinoflagellates in quantity, 

 may also be present. There may be lesser elevations in 

 June and August, due sometimes to one organism or to a 

 small group ; but as a rule there is a period when the 

 plankton is reduced to a minimum in mid-summer and 

 another in mid- winter. 



