SEA-FISHERIES LABORATORY. 301 



plankton and neritic or oceanic) in different localities, bnt : 

 preserved a fairly constant character in each." 



In our second Part, dealing with the observations 

 made from the "Puna" in the summer of 1911, it was 

 shown that in some localities, snch as the north end of the 

 Sound of Mull and the sea around the Small Isles, the 

 phyto-plankton formerly- present was replaced by zoo- 

 plankton, and that the species were more oceanic in type. 

 It was found, however, that still further North, off the 

 north coast of Scotland, and in the Shetland Isles, the 

 phyto-plankton still prevailed even as late as the middle of 

 August. The facts put forward then still seemed to support 

 the view that the most probable explanation of the greater 

 number of Diatoms in the Scottish Seas in summer is 

 that the phyto-plankton remains longer and passes off more 

 slowly as one goes further North. 



Our third Part, published in last year's report, dealt 

 with the observations made from the yacht in the summer 

 of 1912, and again showed, as in 1911, a zoo-plankton 

 with strongly-marked oceanic elements around the North 

 of Mull, where, in 1909 and 1910, we had a more neritic 

 phyto-plankton. During this summer (August, 1912), 

 the Atlantic water carried such oceanic organisms as 

 Doliolum tritonis and Cupulita sarsi as far in as the 

 channel between Mull and Ardnamurchan. Some phyto- 

 plankton was, however, found in August, in the outer 

 Hebrides and in the Sound of Mull. We attributed the 

 greater prevalence of zoo-plankton in part to the fact that 

 in 1912 our observations commenced a month later than in 

 the previous summers, and in part to an unusual influx of 

 Atlantic water, of which there seemed to be abundant 

 evidence.* 



We may remark at once that our observations this year 

 * See last Report, p. 188. 



