Report on the Hydroids. 355 



the same abundance at 20 — 40 m. and at 100 — 200 m.; it may then 

 be placed as if it occurs at ca. 80 m. Under equal conditions the 

 species are arranged according to decreasing frequency (cf. the upper- 

 most 7 species in the table). 



It is worth noticing, that every one of the frequently occurring 

 species only occur in great abundance within rather narrow limits, 

 while they only occur sporadically at less or greater depths. It 

 might be objected here, that when several species have their prin- 

 cipal occurrence in 20 — 40 m., this may be due to the fact, that 

 most collections have been made at this depth; at the same time it 

 has to be noted, that no species occurs in great abundance in 6 — 20 

 m., though we have here 4 stations, whereas Haleciiim miiricatum, H. 

 labrosum, Eudendrium tenellum and in part Cnspidella procumbens, 

 Toichopoma obliqimm and Lafoëa serpens have their principal occur- 

 rence in 40 — 60 m., where we have only one station. But there is 

 naturally some right in this objection, as other conditions, tempera- 

 ture, currents, bottom (vegetation), the apparatus used etc., may also 

 have a disturbing influence; this only means, however, that the 

 results of such a table should not be generalized, until we have in- 

 formation of the same kind from many other dilTerent localities. 

 This information should preferably be given in tabular summaries, 

 after the principle used in table 5. When the material becomes suf- 

 ficiently large, the influence of accidental circumstances could be 

 eliminated, and from the available data we could obtain interesting, 

 general results. It would be very desirable, if such investigations 

 could be carried out on a larger scale than hitherto. 



The use of the indications of frequency will also give information 

 about the power of the different species to adapt themselves to the 

 outer circumstances. Thus, we can readily see, that Lafoëa fruticosa 

 accommodates itself to deeper water more easily than does Calijcella 

 sijringa and Cnspidella procnmbens, although they all belong to about 

 the same depth. 



I shall not go into further details regarding the bathymétrie dis- 

 tribution, as the tables are self-explanatory and speak more plainly 

 than words. 



If it should happen, that some naturalists take note of the above 

 wish, it is certain that they will not all follow one and the same 

 principle in the subdivision of the depths; each will rather arrange 

 the depths in his own manner; the resulting difficulty of making 

 direct comparisons will, however, scarcely be of great importance. 

 I do not recommend the subdivisions I have used as the most cor- 

 rect; as the depths are given in the Journal of the Expedition (see 

 list of stations), it was impossible to classify them in any other 



