2 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



plankton should record their observations, however scanty, so 

 that they may be available for future workers. It is on this 

 account that I venture to offer to the Society some short notes 

 upon plankton observed during the months of August and Sep- 

 tember last off the village of Blackwaterfoot, Arran. I may 

 explain that my object in carrying out these observations was not 

 to look for new species or to collect any great variety of forms, 

 but to investigate the occurrence, and to obtain supplies of 

 properly preserved laboratory material, of forms — especially 

 larval forms — of recognised general importance to the zoologist. 

 The net used was a surface one of the standard size used by 

 E. T. Browne, and composed of bolting silk of sixty meshes to 

 the inch. 



Protozoa and Coelenterata. — As larval forms were the chief 

 objects of investigation, little attention was paid to the above- 

 mentioned Phyla. It should be mentioned, however, that Acan- 

 thometrid Radiolarians occurred occasionally in the surface 

 waters. 



Of Medusae the two commonest forms during August were 

 Phialidium teynporarium, Browne, and Sarsia gemmifera, Forbes, 

 the latter frequently with numerous daughter Medusae budding 

 off from the elongated manubrium, and most frequently with the 

 umbrella turned inside out. Such colonies, as they may be 

 termed, of Medusoid individuals have a wonderfully suggestive 

 appearance in connection with the possible mode of evolution of 

 the highly specialised pelagic colonies so characteristic of the 

 Siphonophore. It seems quite possible that the pneumatophore, 

 or float at the top of the Siphonophore, may have evolved directly 

 from the reversed umbrella of the Medusoid ancestor. 



About the middle of September the beautiful Tiara pileata 

 (Forsk.) became numerous, the specimens mostly being adults 

 with well-developed gonads. 



Nemertea. — Pilidium appeared on only two occasions — on 

 18th August and 18th September. 



Polychaeta. — As was to be expected, there was a considerable 

 variety of larval forms of Polychaete worms. Two attracted 

 special attention. These were the wonderful larva of Chaetop- 

 terus, with its characteristic mesotrochal arrangement of cilia, 



