348 GILMAN A. DREW 
structure that will perform similar acts. When, however, the 
habit and dexterity have been acquired, it is not inconceivable 
that they might be shifted to another closely similar appendage 
if the position of this appendage becomes more suitable forthe 
purpose. The modification is so slight in the arms of most of the 
Decapoda, and the modification varies so greatly in the different 
genera, that it may have been functionally acquired in each case. 
So far as can be seen it would be mechanically quite posgible for 
a squid to use an unmodified arm, instead of the one that shows 
the modification, for the transfer of the spermatophores. The 
spermatophores might not be so tightly or compactly held but 
the normal suckers would hardly seem to interfere greatly in the 
performance of the function. 
There is still another question involved. Is there any genetic 
relation between these two methods of transfer and if there be, 
which, if either, most probably came first? 
A special method of copulation that requires the use of arms and 
complicated spermatophores is not found among animals often 
enough to make it at all probable that it has arisen in this group 
more than once, so we can hardly doubt that the two methods 
are genetically related. 
At first sight the squid’smethod of grasping the spermatophores 
and transferring them directly might be considered the simpler 
process, but there is some reason to doubt that this method was 
at the beginning of the series. While it would be hazardous to say 
that Octopoda were the ancestors of Decapoda, there is much 
reason to believe that the ancestors of the latter lived upon the 
bottom and were far less active than the modern animals. Such 
animals would not seem to be so well adapted for the transfer of 
spermatophores by dexterous movements as the more active, free- 
swimming forms. It is at least certainly true among modern ceph- 
alopods that those that show great modifications in the structure 
of the hectocotylized arms are found entirely among the less active 
bottom forms. If the method of transferring sperm by means of 
the arms originated before the Decapoda became free-swimming 
animals, and this seems the only explanation of its prevalence 
