178 Memoirs of the Indian Museum. [Vol. II, 
British Museum, Oxford University Museum, Cambridge University Museum, United 
States National Museum and the Aberdeen University Museum. 
Before considering the theoretical aspects of the case the following facts must be 
emphasised : — 
1 . The ‘ ' Investigator ’ ’ has trawled 380 times in the deep waters of the Arabian 
Sea and the Bay of Bengal. Twenty-one of these Stations were in water between 
100 and 500 fathoms, in the neighbourhood of the Andaman Isles, — that is to say, in 
situations where we should expect to obtain M althopsis. 
2. Only four of the twenty-one Stations have yielded M althopsis. Some of the 
localities are separated by considerable distances though all are in the neighbourhood 
of the Andamans. The position of the Stations is given on the map (text-fig. 8). 
3. The smallest number of specimens obtained at one Station is four (commu- 
nity C) ; the largest number is ten (community A). The genus is therefore not rare 
at the Stations at which it was ^obtained, but it is not generally common in the 
moderate depths of the Andaman Sea, for not a single specimen was obtained at the 
seventeen other Stations, nor has it ever been obtained elsewhere by the “ Inves- 
tigator.” 
4. The physical conditions under which the four communities live must be 
remarkably similar. 
5. The genus M althopsis is not confined to Indian seas. A number of species 
have been described by Garman from the Pacific Ocean. These, however, must 
represent a separate branch of the genus, for they do not possess the characteristic 
nasal spine. The species M althopsis mitrigar (Gilbert and Cramer) from near the 
Hawaiian Isles possesses this spine. It would be most interesting to know how it 
resembles or differs from any of the five types described here as regards the arrange- 
ment of its ossicles. 
Theoretical considerations. 
It is fortunate that this case can be illustrated by photography so that it lies 
open to the consideration of all, for such wide and definite variation as these com- 
munities exhibit is rarely met with. 
In regard to the change which may take place in organisms, it has been written 
There are two factors: namely, the nature of the organism, and the nature of the 
conditions. The former seems to be much the more important ; for nearly similar 
variations sometimes arise under, as far as we can judge, dissimilar conditions; and, 
on the other hand, dissimilar variations arise under conditions which appear to be 
nearly uniform ” {Origin of Species, page 6, 6th Ed.). There are two reasons given 
here for the statement that the nature of the organism is much the more important 
factor in producing change. The present case forcibly illustrates both reasons. At 
any one of the four localities where, presumably, the conditions are uniform, different 
varieties seem to have arisen, and at any two localities where, presumably, the condi- 
tions might differ, similar varieties have arisen. 
Therefore, as regards M althopsis it may be said that the nature of the organism 
is much the more important if not the only factor in the change that is occurring. 
