A HISTORY OF ESSEX TABLE I Excess of density per 1000 . i-i 8-8 12-9 18-8 22-0 24-5 25-3 26-0 26-5 Larval fish j | Larval Ascidians . Appendicularia . Copepoda 21 171 I J.I 2 124. I 7 86 I 14 108 IO i 204 2 2 IOC 8 QQ Larval Copepoda . Cladocera 3 8 348 2OO 124 39 54 355 28 77 28 Ostracoda iq i I Larval Balani .... Larval Chjetopoda Rotifera I A. i I 18 4 17 149 45 A.Q 83 89 87 '7 43 06 43 33 20 i 8 8 Cyphonautes, etc. . Small Medusae .... Noctiluca
IO 1 / 29 vy 2 I 880 "/ i 5012 7 W I 26 5 i 612 7 383 Totals in 10 gallons . 65 521 1624 316 1259 5397 753 852 543 TABLE II Surface 4 feet Bottom High Low Ascidians IO 2 4. 7 3 Copepoda 78 26 I A.O e-j A.1 Larval Copepoda /* 172 8<5 Q4. jj 2Q TO 118 Larval Balani 28 IO 9 22 66 Larval Chaetopoda Rotifera '3 58 15 I "JO 28 84 8 3 H 1 02 Noctiluca 24.O 7OI 24.2 672 /" "/ Totals eon q6q 601 77o 1018 TABLE III Totals in 10 gallons ( Clear rivers IO , I Heybridge canal 50 Freshwater ,-, , -t , j i- Heybndge basin and ditches 270 . Weedy stagnant ponds I 73 Mean for sea water including the estuaries . . 2060 One great object I had in view was to trace the changes in passing from freshwater conditions down to the sea. The density of the water was therefore determined by observing the excess in weight of the measure of 1,000 grains of fresh water, which is given in the upper line of Table I. In preparing this table I made no distinction between Essex, Suffolk or Kent ; and the results are derived from observations made in the Crouch, Roche, Blackwater, Colne, Stour, Orwell, Aide, Bentley and Medway. As will be seen from Table I. there is a most striking difference in the character and number of the different animals as we proceed from freshwater conditions to the open sea, but there are very few kinds more numerous in this than where the water is less salt. On the whole there are most in the somewhat sheltered estuaries, where the 74
