THE CH^TOGNATHA. 81 



for an extra twenty minutes, as a steamer collided with us in the middle of the operation 

 and stopped proceedings for that period ; it produced five specimens belonging to two 

 species. 



In the diagram, PI. 7, I have endeavoured to express the comparative distribution 

 of Chsetognaths as a whole at all depths, and also some points in that of the common 

 species. (1) The lines labelled decipiens and zetesios merely record the vertical extension 

 of these two species from positive observations (that is, closing and shallow open nets ; 

 the deep open nets being regarded as untrustworthy) : they did not occur in sufficient 

 numbers to give any indication of a centre of distribution. (2) The three diagrams 

 marked serratodentata, furcata i., and hamata i. represent, as ordinates to the curves, 

 the average number of specimens per hour haul by open nets at A^arious depths. They 

 seem to show that serratodentata is most plentiful down to 100 fathoms, furcata most 

 plentiful from 50 to 150 fathoms, and that these upper hamata (which are all very young 

 specimens, p. 76) are numerous between 150 and 300 fathoms *. These three diagrams 

 are all drawn to one scale, and the ordinates to the curves are placed at the lowest or 

 towing-depth of the net. (3) The remaining four curves deal with the closing-net, and 

 are also all drawn to one scale. They are not to be compared with the foregoing curves, 

 because they represent, as ordinates to the curve, the average number of specimens per 

 100-fathom haul of the closing-net at various depths. The ordinates in this case are 

 placed in the centre of the zone studied : thus the ordinate for 150-50 fathoms is drawn 

 on the 100-fathom line. The curve marked /Hrc«i« ii. shows that the population, high at 

 150-50, drops suddenly between 200-100 fms. ; below this zone the species was not 

 captured in closing-nets, and presumably does not occur f. The curve marked hamata ii. % 

 shows clearly enough the influence of a large number of yoimg specimens between 200-100 

 fathoms. Both hamata ii. and m^acrocephala curves seem to show a rise in population 

 between 750 and 500 fathoms, as indicated by the ordinate on the 625-fathom line : this 

 is of course repeated in the curve of general capture of all species. Whether this really 

 indicates a zone of thicker life here or not, will be more easily seen when other groups 

 have been worked out, but I certainly noticed the same rise in population when counting 

 the Copepods in a series of typical hauls. The curve marked " all species together " is a 

 graphic expression of the last column in the table on page 80. Unfortunately it by no 

 ineans agrees with the only previous attempt to deal with the vertical distribution of 

 Chsetognaths as a whole. 



Last year Mr. R. T. Giinther published a paper " On the Distribution of Mid-water 

 Chsetognatha in the North Atlantic during the Mouth of November " (Ann. Mag. N. H. 

 (7) xii. p. 331i). Of his main general conclusions, the most important — namely, "that 

 the upper hundred fathoms contain but few individuals as compared with the deeper 



* The drop in this curve at 200 fathoms, based on a single observation, would probably have flattened out aa 

 indicated by the dotted line if more observations had been taken. 



t The specimens recorded in open nets below 100 fathoms were therefore probably caught in the vertical journey 

 upward : an instance of the deceptiveness of the method of open nets, 



J This includes hamata, var., p. 77. 



13* 



