526 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



The Radiolarians were caught almost equally well 

 by the net owing to their shape and large spines. The 

 Tintinnidae could easily slip through when meeting the 

 net in the direction of their long axis. 



For Diatoms and Peridiniae, &c, the following 

 results were obtained: — 



Silk net Pump, tube 



No. 20 and filter. 



Sceletonema ... 418 



Coscinodiscidae 141 6,444 



Rhizosolenia alata 1,143 4,013 



Chaetoceros Ehrenbergi 44,317 149,793 



Ceratium tripos about equal in each. 



Peridinium divergens 72 317 



globulus 15 1,190 



,, pellucidum 5 1,089 



Coccolithidae 28 11,267 



Dictyocha 54 6,241 



The comparisons for the Protophyta show, therefore, 

 that the constitution of the plankton catch was completely 

 altered by the use of the pump and filter. Out of more 

 than 2,000,000 plants only 110,000 were caught by the 

 net with No. 20 silk, and 9,000 animals out of the one- 

 third million caught by the pump and filter. 



The actual numbers have, however, not so much 

 value, because the smallest organisms give the largest 

 numbers for the loss. If the mass, however, be calculated 

 it is found that the pump and filter gave 52'4 c.cm. as 

 total catch out of 1,000 litres, whilst only 21 c.cm. were 

 caught by the net. 



Hence the constitution of the plankton, formerly 

 determined solely by net catches, must contain greater 

 errors for many forms than were supposed. 



Method of Investigation for the Smallest Organisms. 



It has been demonstrated by several observers that 

 many of the small and fragile forms, without skeleton, 

 are either destroyed completely during the filtration or 



