68 

 Sagitta bipunctata Quoy et Gaimaid. 



According to the recorded occurrences of this species, it would seem to be ecjually at 

 home in a brackish estuary or in the centre of a main ocean, at a mean annual temperature ot 

 about o'^ in the White Sea to 33° in the Red Sea, and from 82° \V. to i 20° E. If this be correct, 

 öiptinctata would be about the most eurythermal, euryhaline, and cosmopoHtan organism known. 



Against such a distribution there is no reasonable argument to allege, but, frankly, I am 

 quite unable to beheve it without more evidcnce. It can only be urged in defence of such 

 incredulity that I know bitterly how ditïicult it is to distinguish between bipnnctata and the young 

 of several other species; this has no such unmistakeable features as some species present. 



The wide extension of the records is due mainly to Levinsen (86) and Steinhaus (96). 

 Of these, Levinsen furnishes only a record of geographical positions without further data. 

 Steinhaus, who shares with Strodtmann the credit of the only recent attempts to gauge the 

 distribution of Chaetognatha, dealt with .several collections, of which some were well, others 

 badly, preserved; among the latter were numerous Indo-pacific records of biptmctata, which I 

 suspect on the ground that this species was not captured by Mr Gardinkr in many months 

 work in the Maldive Archipelago, nor ])y the .Siboga in a year of regular t(nvnettings; this is 

 sufficiently remarkable in an ocean which is stated to have so uniform a jjlankton-fauna as the 

 Indo-pacific. As has already been pointed out (pp. 16, 17) there is every e.xcuse for confusing 

 bipiinctata and badly preserved ncglecta^ which occurs as far north as Japan, and as far south 

 as Java; and the e.xplanaticjn may possibly lie in this fact. It is greally lo be hoped that with 

 the energy displayed at the present time in collecting abroad, and with the increased use of 

 formalin, the extreme records may be either confirmed or refuted. In the meantime it a])pears 

 to be premature to attempt to define the horizontal distribution of this species, and a waste 

 of labour to ])lot the captures on a Chart. 



It is, however, generally agreed that liipuuctaia is a neritic or coast-wisc form, and tliat 

 its oceanic occurrences are rather e.xceptional (Strüutmann, 92 p. 15; Steinhaus, 96 pp. 28,39; 

 FowLER, 05 p. 69). It appears to be euryhaline, and to tolerate a low salinity in the Zuijder See, 

 Hast -Scheldt, at ncarly the longitude of Memel in the Ilaltic, and in the niouth of the Para River. 



As regards the vertical distribution, .Steinhaus records no less than 7 specimens from 

 a closing net 850 — 650 m., at fairly high temperatures (9° 4 to |i2°5]); bul il failcd at greater 

 depths and lower temperatures. In the Research it failed cntirely in all iIk; 35 hauls with the 

 closing net which began at 365 m. or a greater de])th ; that is to sa\- behnv the isolherniobalh 

 of ii°C., which tallies well wilh Steinhaus' record. 



The mere fact that (so far as our evidence at present goes) this temperature appears 

 approximately to set its (k:|)tli-liniit, forms a certaiii anioinil of evitlence against its alleged 

 occurrence in the far north. and suggests that llu- unnanicd ncortlrr for the Russian section 

 of the Con.seil International 04 (i) ma)- ha\'e been tlealing really with arctiia. 



of the cpipl.-inkton of an archipclntjo: for the strong tides and cuncnls gciicratly met wiili in such areas must pioduce ncarly the same 

 cpiplanktonic conditions ihroughout. With the mcsoplankton, however, below the aciion of lide and currcnt, the case is sonicwhal diftcrent: 

 one would not class hamitla^ for vxaniplc, as ncrilic, nierely bcc.ausc it occurrcd in the deep water of an archipelago. The epiplankton 

 of ihc Siboga arca has Iherelore been regardcd in this pliice as neritic, the apparently purely mesoplanktonic species as oceanic. 



