SEA-FISHERIES LABORATORY. 357 



Pseudocalanus and Acartia. The occurrence of these at 

 Port Erin does not quite agree with that recorded by 

 Lohmann for the Baltic. For example, Oithona is 

 essentially an autumn form in the Baltic, and its 

 maximum is in October and November. With us it is 

 more constantly present, and may appear in quantity in 

 various months ; large numbers have been taken in 

 January, July and August, as well as in October. Acartia 

 also seems more widely spread with us, but our maximum 

 in June to July probably corresponds to Lohmann's 

 maximum in May. Pseudocalanus with us appears in 

 quantity in October, and also in May-June, but is 

 apparently not a conspicuous form in the Baltic. 



On the whole, the Copepoda have their greatest 

 abundance with us in early summer (May and June), and 

 again in autumn (September). They were most depressed 

 in '07 and '09 during February and March, and in '08 

 during January, February, July and August. There is 

 usually a marked drop in the Copepoda about mid- 

 summer, and this is sometimes followed (in July or early 

 August) by a vast swarm of one species, such as Calanus 

 helgolandicus. 



As a rule the Dinoflagellate maximum in early 

 summer is later than that of the Diatoms, but precedes 

 that of the Copepoda. In the case of the less-marked 

 autumnal maxima there is less constancy and less regu- 

 larity in the order of succession. 



Some organisms show a remarkable regularity in 

 their time of appearance. For example, the nauplii of 

 Balanus began to appear on February 22nd in '07, on 

 February 13th in '08, and on February 6th in '09. This 

 is one of the cases where it is clear that the normal 

 sequence of events in the life-history of the organism is 

 the dominant factor in determining the constitution of 



