LINNEAIf SOCIETY OF LONDON. 



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Station II, ten miles ofi', the two surface-nets took 40 Podon and 

 75 Evadne each. Other similar cases might be quoted ; but ou 

 the other hand there are diverse hauls on other dates showing a 

 very uneven distribution. The numbers during May and June are 

 relatively high : — 



Podon 190 80 150 100 100 150 



Eyadne 60 80 300 300 300 650 



This is the highest point reached by Evadne, and this form is 

 practically absent, or only occasionally present, during the latter 

 half of August and parts of September. Podon reaches a climax 

 (500) rather later, on August 13th, and soon after that drops to 

 tens and even units, with an occasional appearance (August 31st 

 200) in greater numbers. During most of September the group 

 is but scantily represented ; although neither species is ever 

 absent for long, and occasional larger numbers occur — such as 

 September 19th, off Calf Island, deep net, Podon 70 and Evadne 

 100 ; and September 20lh, Station I, shear-net, Podon 110 and 290, 

 deep net 140, and, at the same time, inside the bay, 182. On 

 September 23rd the ordinary surface-net inside the bay took 550 

 Podon, and the following day 100, after which the numbers fall 

 ofi" rapidly. 



The common species of Oikoj^leura that occurs in our district 

 {0. dioica) is also a form which seems to deserve special notice. 

 It occurs throughout the year, beiug present in every month, and. 

 represented in nearly every gathering. It is absent or rare in 

 the case of the hauls taken on a few dates between August 24th 

 and 28th, and then again on September 4th and 5th. With those 

 exceptions, Oilcopleura is one of the most constant of organisms at 

 all times of the year, and, moreover, is usually present in quantities 

 that range within narrow limits, so that it does not vary to the 

 extent that some Copepoda and Diatoms do. In the winter 

 months — December, January, February and March — the numbers 

 taken are low, but from April to November inclusive quantities of 

 a thousand or two per net are very frequently taken. The highest 

 numbers occur in April, and they only reach 5500 per net, so 

 there is no marked maximum. 



In some cases the numbers of Oilcopleura remain remarkably 

 constant for several hauls, indicating a very general distribution 

 through the water. For example, in one traverse of Port Erin 

 Bay 2780 were caught, and in the return traverse 2030 ; then 

 again, two adjacent hauls gave 3840 and 3600 respectively, and 

 another pair of simultaneous hauls gave 2250 each. But on the 

 other hand, on another occasion, two successive traverses of the 

 bay gave 5050 and 2480 respectively, and other examples of 

 diverse results might be quoted from our records. But on the 

 whole the impression received by an inspection of the records is 

 that Oil-oplei'.ra is more evenly distributed through the water than 

 most of the other common organisms. 



In regard to the horizontal distribution, a mere inspection of 



LINN. see. PROCEEDINGS. — SESSION 1907-1908. d 



