24: 



PROl^. W. A. HBRDMAN : COMPARISON OF SUMBIER PLANKiON 



further south, iu the Irish Sea. A comparison of the collections leads one 

 to the conclusion that in addition to seasonal changes there may be marked 

 local differences in the plankton, so much so as to give a characteristic 

 appearance to the gatherings from certain localities. 



The plankton hauls from the yacht were in all cases taken with the same 

 nets and in the same method, and the after-treatment was also always the 

 same ; so that the various gatherings are as nearly comparable as is 

 possible. All the vertical hauls were made with the smaller " Nansen " 

 net, a closing-net (fig. 1) of no. 20 silk, with the mouth 35 cm. in diameter. 



Fig. 2. — Lucas Sounding-Machine as used with Nanseu Vertical 

 Closing Net on ' Ladj'bird.' 



Surface gatherings were sometimes taken at the same time with ordinary 

 open surface tow-nets made of the same silk as the " Nansen " net and of 

 approximately the same size. The Lucas Sounding-Machine (fig. 2) fitted 

 with 200 fathoms of pianoforte wire was found to be most convenient and 

 expeditious in taking these deep vertical hauls. 



The temperature of the surface water of the sea in the Hebrides varied 

 this summer during the month from 11-8° C. on July 11th, off Canna, to 



