\l \ N X DIATOMS OF THE A.LBATROSS VOYAGES. 223 



known. Only when each species is mounted by itself and in such a 

 position on the slide as to be instantly found under the microscope 

 can diatom preparations be considered worth} to be compared with 

 other scientific specimens of reference. 



In addition to these preparations of single forms, representing each 

 species round, this report is accompanied l>\ a series of group slides 

 of selected forms. Each of these preparations has from 10 to LOO 

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

 of the india ink ring. Their purpose is to afford a type gathering of 

 each of the more importanl diatomaceous dredgings and soundings 

 examined. 



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

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

 ples included most of those obtained at gread depths, say 1,200 fath- 

 oms and upward. There are, however, many cases where deep 

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

 3607, having a depth of 987 fathoms, and 3712H, at 1,71! fathoms. 

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

 in shallow water and at points where diatoms would naturally be 

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

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

 gatherings and in many of those from shallower places or from the 

 sea surface thai none were present at these points. In many 

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

 these gatherings were made. It is evident thai devices perfectly 

 adapted to securing larger forms of animal and vegetable life may 

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

 The modes of making the gatherings, the way they are broughl aboard 

 t lie* ship, and the process of assorting the contents would often elimi- 

 nate all traces of the diatoms, at least of all forms thai er<>\\ R ithoul 

 attachment to other bodies. Diatoms are to he found in richest 

 quantity in the upper and lighter layers of mud of the sea bottoms, 

 and those on the surface of the sea can be secured only when a special 

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

 majority of the gatherings now in the possession of the CJ. S. 

 National Museum. are destitute of diatoms, although many of them 

 were made at points where with different methods rich supplies could 

 have been secured. The cruise of the Albatross under \)v. Alexander 

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

 obtaining an unusually rich supply of the diatoms. 



I have tried to supply this deficiency of diatomaceous material in 

 some of the dredgings by examining the contents of the stomachs of 

 animals, chiefly holot hurians, taken at these points. This is, how- 

 ever, a very partial and unsatisfactory subsl it ute. The stomach eon- 

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



