215 
1896-97.] Mr George Murray on Marine Diatoms . 
the 6th of April, a haul of the tow-nets simultaneously at the surface, 
five, twenty-five, and fifty fathoms in the deep water of Loch Fyne 
between the Otter and Tarbert. This haul was remarkable, not 
only for the large number of Coscinodisci it yielded with one each 
inside, but the individuals from the surface and five fathoms very 
frequently had their contents divided into eight and sixteen 
rounded-off portions, as in figs. 2, a, b, and 3. Mixed with these 
were a large number of packets of young Coscinodisci and large 
empty frustules. Even down at twenty-five fathoms the number of 
packets was almost as great as at the surface and five fathoms. 
Where the cell-contents were divided into eight, the eight portions 
were each nearly twice the volume of those in the cells which had 
divided into sixteen. At first I naturally jumped to the conclusion 
that the eight and sixteen rounded-off portions were the outcome 
of free cell-formation, but a more minute study has convinced me 
that they are produced by successive divisions into two. The 
relative positions of the portions as shown in fig. 2, a , and even 
more strikingly in other instances I have seen and photographed, 
point to this mode of formation. The association of these with 
the packets, the correspondence in size of the eights and sixteens 
respectively, the adequacy of these divided portions to the formation 
of the packets, as indicated by the undivided instance of BiddulpMu 
mobiliensis, the occurrence of two young Coscinodisci within a 
parent frustule, all lead irresistibly to our interpreting the divisions 
of the contents as preliminary to the formation of the packets. 
Granting this to be the explanation, I next found myself in face 
of the difficulty of accounting for the future progress of the young 
Coscinodisci. Diatoms, we are accustomed to be told, go on 
decreasing in size by the breadth of the girdle membrane at each 
succeeding ordinary division until a minimum size is reached, when 
the formation of an auxospore re-establishes them at the maximum. 
This is true enough, but it is generally associated with the statement 
that, owing to the rigid silicified nature of their membranes, 
individual diatoms are incapable of superficial growth. I am by 
no means sure that this last statement has any greater value than 
a likely assertion, but if it be true, liow then would it fare with 
these small Coscinodisci , launched into the world at what must surely 
be their minimum size? Would they start life with the formation 
