342 PLANKTON OBSERVED AT PLYMOUTH. 



occurrence of several species in " tolerable abundance ^' amongst 

 tbem an Acanthometron, whicb may be identical with mine. On no 

 otber occasion bave I seen Radiolaria at Plymouth, and this sudden 

 appearance, together with that of the other organisms mentioned, 

 very probably indicates that the surface-layers of the sea with their 

 plankton are displaced through considerable distances by the pro- 

 longed or powerful action of the wind in one direction.* It is desir- 

 able that this observation should be extended and confirmed, as it 

 has obviously an important bearing on the distribution of the food of 

 migratory fishes like the herring and mackerel. 



July 2Srd. — Saphenia mirabilis, Haechel, was taken at the bottom in 

 9 fathoms off Penlee Point. The specimens were of the same size 

 as those recorded by Mr. J. T. Cunningham in this Journal, vol. ii, 

 page 194. The haul also contained a number of Irene viridula, 

 Eschsch., a medusa which was almost invariably present in the bottom 

 tow-nettings from June to August. Once only did they appear in a 

 surface netting, and that was one taken soon after midnight on July 

 21st in Start Bay. 



August 2Qih. — The Siphonophore Muggisea atlantica, Cunningham, 

 made its appearance. The eudoxomes were at this time immature, 

 and were not observed to be detached until September 2nd, when 

 they bore ripe sexual products in the manubrium of the genital necto- 

 calyx. Later on (23rd September) I found the young Calyconula 

 larva corresponding to a figure by Chun in the Ann. and Mag. Nat. 

 Hist., ser. 5, vol. xi, pi. v, fig. 6. This was at a time when the 

 adult oocurred in very large numbers, and just before it began to 

 become scarce. 



September bth. — The pelagic larva of the interesting Polychaste, 

 Magelona papillicornis, Fr. Mull., was plentiful for a fortnight after 

 this date, and then began to diminish in numbers ; at the end of the 

 month only stray specimens were found. 



September 10th. — Young Amphioxus larvaa were taken just outside 

 the Breakwater. A few more at a slightly later stage were taken 

 on 13th and 17th September, with sixteen to seventeen primary 

 gill-slits. 



September 2Srd. — MuUer's larva (Polyclad) was first noticed and 

 was frequently found during the ensuing week. In August and 

 September the surface tow-nettings often contained a young Poly- 

 clad, probably Leptoplana, from H to 2 mm. in length. 



September 2^th. — The absence of Noctiluca is a very extraordinary 

 feature of the year, for 1891 was remarkable for the immense pro- 



* Dr. John Murray informed me that Radiolarians had not been taken in the Clyde area 

 until I found them, after the prolonged south-westerly gales of 24th to 26th August, in a 

 tow-netting taken from the yacht " Medusa," off Rothesay, Bute. 



