6 Dr. G. C. Wallich on the Diatomacea. 



matter, answers all their requirements, and prepares them, in 

 due course, to become food for creatures far removed from them 

 as regards complexity of structure. 



The pelagic Diatomacese have hitherto escaped detection 

 chiefly because the means employed for the purpose have been 

 inadequate. Indeed, their detection at all may be said to have 

 been the result rather of accident than of any systematic endea- 

 vour to trace out the boundaries of their distribution. 



The Diatomacea3 abound in all waters, more or less, but no- 

 where in such vast profusion as in the open ocean. Their pre- 

 sence there is in nowise accidental, or necessarily associated with 

 that of foreign floating bodies, such as drift-weed, wood, &c. &c. 

 It is well known that a large class of Diatoms consists of what are 

 called "free forms," that is, of frustules possessing neither stipes 

 nor mucous cushion or pedicle of any sort, whereby they might 

 attach themselves to, or derive support from, other bodies ; and 

 that they are moreover endowed with a very peculiar and remark- 

 able power of motion. 



To these "free forms" belong the Diatomacese of the open 

 sea ; and there cannot be a doubt that the numbers in which 

 they exist, in all latitudes, at all seasons, and at all depths (ex- 

 tending from an inch to the lowest limit at which the most 

 attenuated ray of light can penetrate, or at which pressure per- 

 mits), are immeasurably in excess of what we have hitherto been 

 in the habit of assuming. 



Nothing is more perplexing to the collector, at sea, than the 

 apparently capricious manner in which the minute forms of or- 

 ganic life, both vegetable and animal, present themselves in and 

 disperse from the surface waters. I have repeatedly observed 

 the upper portion of the sea to burst forth suddenly, as it were, 

 into a swarm of living particles, and these again as capriciously 

 and suddenly to disappear. At one time, a slight change of 

 temperature, or wind, or cloud, brings about such a result; 

 at another, it follows upon influences unappreciable perhaps 

 to our organs of sense, but at once indicated by barometric 

 changes. During calms and bright sunshine, as might be anti- 

 cipated, the assemblages of these vast masses of life are most 

 frequent and constant, and especially so in the case of the Dia- 

 tomacese ; but this is by no means the invariable condition, 

 ^,s shall presently be shown. 



My attention was, in the first instance, drawn to these remark- 

 able objects by the phajnomenon which presented itself in the 

 Bay of Bengal and Indian Ocean, in March and April 1857. 

 This consisted of an immense multitude of small yellow flocculi 

 and tufts, with which the surface of the sea for some depth 

 jvas crowded in sufficient quantity to impart to it a faint 



