102 Transactions of the Royal Society of South Africa. 
If reduction of the fin in length to its present dimensions can thus be 
accounted for, how can we explain the relative elongation of its base of 
attachment to the body ? Apparently this cannot be explained as an effect 
of use of this portion of the fin, for, as noted above, in the early stages this 
feature is well marked, though the organ is functionless. It is then merely 
a dermal membrane in which rays are not developed. It may be borne in 
mind, however, that the paired as well as the unpaired fins arise in this 
way, the membrane being replaced by the permanent fin, whose base of 
attachment to the body is, as a rule, relatively shorter. The presence of a 
well-developed though functionless pectoral fin of this nature at an early 
stage may therefore be accounted for by the facts, or rather the mechanism 
of development. 
A modification of the body acquired in this way by functional and 
environmental changes would be hard to distinguish from a germinal or 
" innate " character. 
The question as to whether such acquired characters may become fixed 
in another way, viz. by so affecting the germ -cells that they would be repro- 
duced in succeeding generations, if their original cause were removed, is 
another though quite legitimate inquiry, namely that of the inheritance 
of acquired characters. 
There are so many pitfalls to be avoided in the discussion of the question 
of heredity, largely due to the use of terms not strictly defined, that one 
must walk warily. Thus the word " environment " has been here used in 
two senses, first as the external surroundings (physical and biological) of the 
body as a whole, and secondly as the external surroundings of an organ of 
the body, including the other organs. It is necessary to use the term in the 
wider sense, for the change in position may not have been in direct co-ordi- 
nation with a changing external environment, but with some gradual 
internal change in the organs of the animal itself. With this explanation 
it will probably be admitted that the acquired characters referred to are 
transmitted, or rather repeated in succeeding generations, for the same 
cause acting under the same conditions will produce the same effect. It 
may even be admitted that the changed environment so defined may become 
so complex and fixed that these characters will be indistinguishable from 
hereditary characters, acquired by a process of natural selection of favour- 
able variations which have not been brought about by use and disuse. In 
this particular case it is not at all obvious that the new organ is of any great 
advantage to the animal. On account of its accidental position near the ebb 
and flow of the current of water at the opercular opening it is kept in 
activity, and, so long as it does not seriously interfere with the normal 
functions of the body, its continued existence will be tolerated. Other 
cases apparently of this nature are known in the animal kingdom, and 
perhaps this may be added to the list. 
