20 VARIATIONS IN NUMBERS AND HABITAT OF 



over great distances. In such cases it is not a question of 

 occasional inspection or of looking for them or dredging, since 

 they are visible at any time in suitable weather from the deck of 

 the yacht, when they are present. There seems to be great 

 variation in the numbers of the very common Medusa, Amelia 

 auvita, in different years, unless it be that in some years they 

 swim near the top and in others low down out of sight. This 

 they certainly do according to the weather, coming towards the 

 top when fine and smooth, but such a difference could scarcely 

 occur throughout an entire season. In July, 1888, I saw in the 

 course of a few days in the Aide below Orford, more deep blue 

 specimens of Cyanea lamarkii than I have seen any where before or 

 since, though year by year I have looked for them most atten- 

 tively and not seen one. This handsome species had not been 

 previously observed within some hundreds of miles of the English 

 coast. Many years ago I saw at Queen borough a great many 

 specimens of the beautiful Medusa, Chrysaova isoceles, but lately I 

 have year after year seen comparatively very few. Last year 

 (1900) I think they were somewhat more common ; but, strange 

 to say, they were all a very pale variety, with none of the dark 

 radiating stripes on the upper surface. In the last few years 

 good fine specimens of Plenrohranchia pileus have been more and 

 more scarce, whereas formerly they were common. Time alone 

 will show whether such changes as these just described are 

 permanent or only temporary. The great variation in the 

 numbers of fish and shrimps is, of course, well known. 



Of a totally diflferent character is the remarkable occasional 

 appearance of Heteronereis. I have never found specimens in 

 mud, but in dredging I have obtained a few, very imperfectly 

 developed. I have occasionally found them in my aquarium, 

 into which they must have been introduced when young, living 

 in tubes amongst algae, before assuming the adult form. The 

 remarkable fact is the manner in which they are now and then 

 seen swimming at the surface of the sea water. I must have 

 lived at anchor in tlie Orwell and Stour for a total period of 

 between one and two years, and yet I never saw Heteronereis in 

 that locality except ofT Harwich on July i6th, 1898, and perhaps 

 once in the Orwell at Pin Mill. I do not know how early they 

 appeared, but from the time I turned out at 5 a.m. until 7 a.m., 

 they were swimming about on the surface in such numbers that 

 they were only a few yards apart, and, as I judged over an area 



