542 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



" Challenger " in the warmer seas, but since these were 

 only qualitative catches, no comparison could be made, 

 and we are faced with another problem — What condition 

 is it in the sea which makes it more favourable for life 

 in the colder regions? This has been referred to in an 

 important paper by Brandt (9), which should lead to 

 further investigation. 



The catches, however, made in the cooler regions are 

 in reality much smaller than they appear, because the 

 bulk of the organisms present are diatoms. When the 

 volume of plankton is estimated by allowing the catch 

 to settle down for 24 to 48 hours, an easy, but not always 

 reliable method, it will be seen that a diatom catch refuses 

 to sedimate as one where Copepoda or Ceratium are 

 present. Thus a diatom catch appears to have a much 

 greater volume than is really the case, even after it has 

 stood for weeks. Furthermore, as Lohmann has since 

 pointed out, the presence of diatoms in considerable 

 quantity increases enormously the catch because the 

 diatoms entangle themselves over the meshes of the net, 

 and render it a much finer filtering tissue. 



In the tables given in the published results of the 

 expedition there is in one case an increase in the catch 

 between the stations of from 5 c.cm. to 156. This sudden 

 increase was due to Calanus finmarchicus ; and one must 

 evidently consider this as a swarm. The nearest land was 

 500 miles distant, and, after the large catch, the catches 

 at the following stations again showed quite a small 

 volume. 



It is a well-known fact that the Siphonophora, 

 P or pita and Velella, are found travelling in great shoals 

 together, and in the accounts of the expedition we find 

 that south of the Cape Verde Isles shoals were very 

 frequently met with, amongst which occurred swarms of 



