344 DEPTHS OF THE OCEAN 



dimensions and of reproducing their kind. The degenerate 

 forms of neritic diatoms met with in the open sea appear to 

 me to lack the stimulus which in some unknown manner leads 

 to the formation of auxospores ; consequently their ultimate 

 extinction is only a matter of time, even though they may 

 continue reproduction through a whole succession of genera- 

 tions. This is, of course, merely an unsupported surmise, for 

 the few random investigations we have hitherto made do not 

 afford sufficient material to settle questions of this nature at 

 all definitely ; but my idea is that the hypothetical views of an 

 author are of more value than the enumeration of solitary facts 

 that have no apparent connection. 

 Resting-spores When the neritic diatoms evolve resting-spores out in the 

 sea^^^°^^^" open sea, which occurrence w^e have been able to observe on 

 more than one occasion, it might be supposed that the spores 

 would be destroyed after sinking down to profound depths. 

 This is not, however, necessarily always the case, since they 

 appear to sink slowly, and remain within the region of light 

 for weeks if not for months. The spores after leaving their 

 cells are so minute that they are rarely caught in silk nets, 

 so that little has been done as yet to throw light upon this 

 question. But now that we have adopted the centrifuge- 

 method it is possible to collect them, and we discovered numbers 

 of resting-spores of species of Chcstoceras in our centrifuge- 

 samples from the Atlantic. In a litre of sea-water from Station 

 87 (lat. 46° 48' N., long. 2f 46' W.), from a depth of 100 

 metres, I secured altogether. 1 160 resting-spores belonging to 

 three different species of ChcBtoceras, though the forms them- 

 selves were not present at that time in a vegetative state either 

 in the surface-layers or deeper down. Most probably what we 

 got were representatives from the last remnants of the diatom- 

 masses that throng the surface-layers there during the spring. 

 Distribution. Nentic species include a very large number of diatoms — 



a class by far the most characteristic in coastal seas. In the 

 majority of these neritic diatoms we have now been able to 

 prove the existence of resting-spores. The peridinece, on 

 the other hand, are mainly oceanic, especially the species of 

 Ceratmni. One of the best-known neritic peridineae is the 

 comparatively low species Prorocentrimi micans ; but there are 

 probably, too, whole series of small forms, as yet imperfectly 

 known, which prefer the neighbourhood of the coasts. The 

 coccolithophoridse, again, are undoubtedly oceanic, whereas 

 most of the naked flagellates are most likely domiciled in 



