32 



PROF. W. A HERDMAN : COMPARISON OF SUMMER PLANKTON 



July 13, '09 

 „• 14, '10 

 „ 19, '10 



July 18, '07 



„ 28, 08 

 , 28, '09 



Date. 



Depth 

 IN Faths. 



No. OF 



Hauls. 



Zoo- 



or 



Phyto-Plankton. 



Remarks. 



Off Canna, Rum, S^'C. 



130 

 80, 105, 128 



85 



104 



83 & 95 to 105 



100 to 106 



,July28&29,'08| 

 29 '09 



July 26, '07 

 „• 27, '07 

 „ 30, '08 

 „ 30, "09 

 „ 31, '08 



Aug. 1,'10 



64 to 66 

 70 



76-80 

 76 

 95 

 80 

 54 

 70 



P. 

 P. 

 P. 



Skate Island. 



Z 

 Z 



z. 



Fyne. 



Z. 

 Z. 



With some small Copepoda 

 and a few other small 

 animals. 



Upper Loch 



Arran, Sound of Bute, Si'C, 

 1 Z. 1 



1 . ^.• 



1 Z. (mixed) 



1 Z. 



2 Z. (mi.\ed) 

 1 1 P. 



Diatoms also present. 



A few Diatoms. 



A few Diatoms and Peridiiiians 



Copepoda, &c., present also. 







Irish Sea.— 



-Mid-Channel. 





Apr. 7, '09 . . 



60 



4 



P. 



\ Typical spring pbyto-Plank- 



„ 8, '09 . . 



60 



5 



P. 



J ton. 



Aug. 6, '09 . . 



59 to 60 



5 



Z. 





„ 7, '09 . . 



60 to 70 



4 



Z. 





„ 10, '09 . . 



60 to 73 



4 



Z. (mixed) 



^ 



„ 17, '08 . . 



60 to 70 



6 



Z. (mixed) 



^ A few Diatoms present. 



„ 24, -07 . . 



60 



10 



Z. (mixed) 



Sept. 4, '07 . . 



60 - 



12 



Z. 





„ 12, W.. 



60 



6 



Z. (mixed) 



j Diatoms getting more nu- 



„ 12, '08.. 



60&70 



2 



Z. (mi.xed) 



1 merous. 



Thus we have evidence that, off the north-\vcst coast of Scotland at one 

 time of year (July), in several successive years the plankton, as sampled 

 by vertical hauls, was o£ different types (zoo- and phyto-plankton) in 

 different localities, but preserved a constant character in each. 



Now, in the Irish Sea, around the Isle of Man, when the plankton o£ the 

 whole year is considered, it is clear that neighbouring localities do not present 

 widely different characters as tliey do in the Hebrides, and that a zoo-plankton 

 and a phyto-plankton do not occur simultaneously a few miles apart. In 

 spring or early summer, in the Irish Sea, as elsewhere, there is an enormous 

 phyto-plankton maximum (se'^ Table, p. 35, column D), which gradually 

 dies away, and is replaced by the zoo-plankton which is characteristic of the 

 summer months (Table, col. E). In September or October, again. Diatoms 

 make their appearance in profusion, constituting a second, autumnal, phyto- 



