SUMMARY OF RESULTS. 
1453 
The general results bearing on the distribution, in the different zones of depth, 
of the Benthos animals procured by the Challenger, as well as their distribution 
in the three great zones of latitude above indicated, are exhibited in Tables I. and II. 
on page 1430. An examination of Table II. shows that the species common to all 
the three zones of latitude on the whole increase in number as the depth of the zone 
decreases, and the same is true of the species taken only in the northern and southern zones 
and not within the tropics ; the increase is not quite regular throughout the shallower 
zones, owing, apparently, to the relatively small number of species preserved from the 
Challenger’s dredgings in the shallow waters of the northern temperate regions. 
The percentage, however, of the species from any one zone of depth which are common 
to all the three zones of latitude or to the northern and southern zones and not present 
within the tropical zone, is less in the shallower than in the deeper zones. In all the 
deeper zones the number of species from any one zone which occur in all the three 
zones of latitude in any depth whatever does not exceed 9 per cent, of the total 
number taken in that zone of depth. For instance, of the 153 species taken in depths 
beyond 2500 fathoms, only 14 species are found in all the three zones of latitude, viz., 
the tropical, northern, and southern zones ; 8 are common to the northern and southern 
zones, but do not occur in the intervening tropical zone ; 5 are common to the tropical 
and southern zones, and 6 common to the tropical and northern zones. Again, of the 493 
species taken in the zone between 1000 and 1500 fathoms, only 34 are common to 
the three great zones of latitude in any depth whatever, 28 are common to the northern 
and southern zones, 26 common to the tropical and southern zones, and 48 common 
to the tropical and northern zones. It thus appears that only a relatively small 
percentage of Benthos animals have a very wide distribution over the floor of the 
ocean. 
If, for illustration of this subject, we limit our attention to the species captured in 
the southern zone of latitude, that is, to the south of the tropic of Capricorn, we find 
that about 3000 species were procured by the Challenger at all depths, belonging 
to about 1250 genera. The number of species actually described and recorded in the 
special Zoological Eeports amounts to 2814 species, belonging to 1179 genera. 2476 of 
these species belonging to 949 genera were taken in this southern zone only, while 338 
species belonging to 230 genera extend into one or both of the other great zones of 
latitude, hence 88 per cent, of the species captured are limited to the southern zone, 
while only 12 per cent, extend to the tropical and northern zones. An analysis of the 
above lists shows that 172 species, or about 6 per cent, of the species captured in the 
southern zone, are recorded in the reports from the northern zone, but not from the 
intervening tropical zone. This points to a greater similarity between the widely 
separated polar zones than between contiguous zones. The similarity would be still 
more striking had representative species of genera occurring in the northern and 
(summary of results chall. exp. — 1894 .) 183 
Comparison of 
THE Distribution 
of Species in 
DIFFERENT ZoNES 
OF Latitude and 
DIFFERENT ZoNES 
OF Depth. 
Distribution of 
Species Captured 
South op the 
Tropic of 
Capricorn. 
