MARINE ZOOLOGY 



Crustacea or the Mollusca. Those of Essex are from my own list, 

 including those collected by Mr. Hope and Mr. Unthank : 



It will thus be seen that there is a remarkable difference, and that 

 whilst fifty-eight species found in Essex are not found in Norfolk, and 

 forty-seven in Norfolk not in Essex, there are only thirty-nine common 

 to both. These results are no doubt in part due to imperfect collecting, 

 but yet, I think, still more to the materially different characters of the 

 coasts. 



MARINE AND FRESHWATER PLANKTON 



During the years 1882 to 1889, from the early part of May to the 

 middle of September, I carried out continuous observations of the num- 

 ber of small free-swimming animals per gallon of water. The method 

 adopted was to collect the water near the surface, half way down and 

 near the bottom, in a bottle sunk empty, and filled by pulling out the 

 cork. Usually 2\ gallons were collected, and passed through a fine 

 sieve, not allowing any animal larger than ^ of an inch in diameter to 

 pass. The material so separated was then washed out by pouring a 

 few ounces of sea water on the back of the sieve, care being taken that 

 none of the animals should be killed by drying. I had a glass trough 

 3 inches deep, i inch broad, and | inch from front to back, into which 

 the water containing the animals was poured, and the number of the 

 various kinds counted, the process being repeated until the whole had 

 been examined. The different sorts could in general be easily dis- 

 tinguished by their different form or manner of swimming. It would 

 be out of place to go into detail, but it seems desirable to give some 

 of the general results which, though never printed, were repeatedly 

 described by me in public lectures at a time when this subject had 

 attracted little or no attention. 



In the following tables I give the number of the animals per 

 10 gallons of water, but omit those which on an average do not amount 

 to one in that quantity. These were determined from my first three years' 

 observations, and might be somewhat modified by the later, which have 

 not yet been adequately discussed. As might be expected larval forms 

 play a very important part. 



73 



10 



