284 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



with what has been recognised by naturalists for many 

 years, that strong currents are favourable to a profuse 

 development of animal life. 



A further point thai has si ruck us in the progress of 

 this investigation is the obvious distribution of at least 

 some organisms in shoals. This ran occasionally be seen 

 by the eye, when, for example, shoals of large Medusae 

 are encountered which are so abundant for a limited area 

 that on a calm day they may cover the surface like a 

 tessellated pavement, and assume polygonal forms from 

 mutual pressure. On other occasions our nets have 

 evidently encountered swarms of Copepoda, of Cirripede 

 Nauplii, of Crab Zoeas, of worm larvae or of other 

 organisms. One might expect such results in the case of 

 neritic forms, which are merely stages in the life-history 

 of some gregarious organism; but the occurrence is by no 

 means confined to such, it extends in our experience to 

 oceanic organisms on the high seas, and this sporadic 

 distribution in swarms has not been sufficiently taken into 

 account by some writers who have treated of the 

 distribution of the plankton in recent years. 



The enormous quantities of the Diatom Thalassiosira 

 nordenshioldii, Cleve, in our collections early in April 

 (e.g. on April 4th 1,750,000, on April 5th 2,000,000, on 

 April 8th 1,350,000 in single hauls) are a noteworthy 

 feature. According to Gran (" Nordisches Plankton," 

 Lief. Ill, xix, p. 16), this is a northern species 

 found on the coasts of Northern Europe and the 

 east coast of America. We have not met with it in 

 the Irish Sea before. It might be argued that 

 this was a case of a more northerly species carried 

 down into our area by exceptional circumstances, or on 

 the other hand the explanation may be that the Irish Sea 

 is within the normal range of the organism, and that 



