R. E. Eloyd : Deep-Sea Fish caught by the “ Investigator F 
179 
1909.J 
If these five types are separate species in the ordinary sense of the word, they 
must, according to some theorists, have primarily arisen each in a separate locality, 
in adaptation to some peculiarity of that locality by natural selection from among a 
population exhibiting minute variations, and subsequently come together to exhibit 
the remarkable intermingled distribution obtained. This seems highly improbable. 
It seems more likely that the type v, the true Malthopsis lutea ^ is an established 
species, which during a long period of stability has become widely distributed in 
moderate depths of the seas around India. One specimen of this type was taken by 
the “ Valdivia ” off the east coast of Africa. It is especially common at certain 
points in the Andaman Sea. Among the offspring which the members of the species 
are producing are some which differ widely from their parents as regards their shape 
and dermal ossicles, the differences being of particular kinds. Offspring showing 
the same kind of differences from their parents are being produced in widely sepa- 
rate localities. Judging from the fact that the type w occurs in each of the four 
communities, it may be assumed that it is a hardy and progressive form which is fast 
becoming established as a new species. 
This is put forward as an explanation of the manner in which change is sup- 
posed to be taking place. As to the cause of the change nothing can be said from 
the evidence, except that it seems to be inherent in the organism and quite indepen- 
dent of the conditions of environment. 
In many ways the phenomenon calls to mind that observed by De Vries in the 
plant Œnothera, a phenomenon which that author terms “Mutation.” This term 
defines the manner in which evolution is believed to occur ; by using it one allows 
exceptions to the rule that a parent and its offspring must be of the same species. So 
far as I can understand it, the Theory of Mutation does not deal with the causes which 
lead to the appearance of these exceptions, but emphasises the fact that the nature 
of the organism is a much more important factor in their production than the external 
conditions. 
An important part of the Theory of Mutations is the idea of characters as 
definite units; an idea which seems to rest on the surest evidence. These fish 
illustrate this and moreover show how some of the character units are related to one 
another. 
It has been shown that there are two types of subopercular spine among the 
collection, and that a particular type of spine is always associated with a particular 
arrangement of the dermal plate ; that there are certain types in the form of the 
disk which are quite independent of the character of the derma, for one specimen 
(A 4) has preserved the narrow form but acquired the orderly character of the derma 
completely, while others (C 2, C 4) have lost the narrowness but retained the disorderly 
derma. It has also been shown that the nasal spine is quite independent of the 
subopercular spine, for all the specimens, whatever the form of their subopercular 
spines, possess nasal spines approximately of the same size and form. This is the 
opposite of what we might expect, for the nasal spine is a character peculiar to one 
branch of the genus Malthopsis, while the subopercular spine in various forms is 
