MANX DIATOMS OF THE ALBATROSS VOYAGES. 223 



known. Oiil}^ when each s])ecios is mounted by itself and in such a 

 position on the sKdo as to he instantl}' found under the microscope 

 can diatom i)reparations he considered worthy to be compared witli 



other scientific specimens of reference. 



In addition to these preparations of shigle forms, representing each 

 species found, tliis report is accompanied by a series of group slides 

 of selected forms. Each of these pre[mrations has from 10 to 100 

 diatoms, arranged in rows on tlie cover glass or massed in the center 

 of the india ink ring. Their i)urpose is to afford a type gathering of 

 each of tlie more inijjortant diatomacoous dredgings and soundings 



exannncd. 



As has been remarked, a large number of the Albatross gatherings 

 were found to be destitute of diatoms. Naturally, these barren sam- 

 ples in(dud(Ml most of those obtained at grca-t de])ths, say 1,200 fath- 

 ojns and u})wartl. There ar(>, however, many cases where deep 

 dredgings were particularly rich in diatoms, as, for example, station 

 3607, having a deptli of 987 fathoms, and 3712II, at 1,744 fathoms. 

 It was also found that a considerable number of tlie gatherings made 

 in shalh)\v water and at points where diatoms would naturally be 

 looked for contained no trace of them. It wouhl certainly be a mis- 

 take to infer from the absence of diatcmis in most of the deep-sea 

 "■atherin^'-s anil in manv of those from shallower places or from the 

 sea surface that none w^cro present at these points. In many 

 instances their absence is to be explained by the methods by which 

 these iratherinirs were jnade. It is evident that devices perfectly 



.^.^.v . .,.j_, 



adapted to securing larger forms of animal and vegetal)le life may 

 fail completely to retain any specimens of these very minute plants. 

 The modes of making the gjitlu^rings, the way they are brought aboanl 

 the ship, and tlie process of assorting the contents would often elimi- 

 nate all traces of the diatoms, at least of all forms that grow without 

 attachment to other bodies. Diiitoms are to be found in richest 

 quantity in the upper and lighter la^xrs of mud of the sea bottoms, 

 and those tjn the surface of the sea can be secured onl}^ \\\\c\\ a .special 

 apphance is attached to the tow nets. As a consequence, a large 

 majorit}- of the gatherings now in the possession of the U. S. 

 National^Iuseum are destitute of diatoms, although many of them 

 were made at points where with different methods rich su])plies could 

 have l)een secured. The cruise of the Albatross under Dr. Alexander 

 Agassiz, just completed, is reported, however, to have resulted in 

 obtaining an unusually rich supply of tlie diatoms. 



1 have tried to supply this deffciency of diatomacoous material in 

 some of the dredgings l)y examining the contents of the stomachs of 

 animals, chieffy holothurians, taken at these points. This is, how- 

 ever, a very partial and unsatisfactory substitute. The stomach con- 

 tents are generally rich in diatoms, so far as number of individuals 



