SEXUAL ACTIVITIES OF THE SQUID 347 
and wherever found it is always the third arm that is involved. 
Sometimes this arm is on the right and sometimes it is on the left 
side. In three genera it is known to be caducous and in a fourth 
(Alloposus) it is supposed to he. In the remaining genera in which 
the hectocotylized arm has been studied, the modifications, while 
not resulting in the actual separation of the arms, are of an exten- 
sive nature. In Octopus, for instance, they involve not only 
changes.in size, form, and the condition of suckers, but a special 
eroove is present through which the spe matophores are supposed 
to be carried from the base, presumably from the penis to the tip. 
The tip in turn is modified so it is supposed to function in placing 
the spermatophores in position for ejaculation. 
The Decapoda do not show such extensively modified hectoco- 
tylized arms. ‘The changes are here chiefly confined to some of 
the suckers and their immediate vicinity. In Loligo this modi- 
fication apparently serves to aid the armin grasping thespermato- 
phores, which are then transferred by the movement of the arm. 
While the actual grasping of the spermatophores has not been 
previously observed, there can be little doubt that other forms of 
the Decapoda use the arms in a similar manner. Where copula- 
tion has been observed the movements of the arms indicate that 
they are used in the transfer, and the positions of the sperm reser- 
voirs that have been found attached to the females indicate that 
some arm must have functioned in getting them into position. As 
there is no special transferring mechanism, this must have been 
accomplished by the free movements of the arms. 
Where structural modification is slight and the placing 0 the 
spermatophores is due to dexterity, there is less difficulty in under- 
standing how the function may be shifted from one arm to another 
in response to changes in the positionof the attachment of the 
reservoirs on the female, than would be the case were great 
structural changes involved. It would be much more difficult to 
understand how there could be a shifting in series of arms as highly 
modified as those of the Octopoda, where only the medified arm 
could possibly perform the function. 
It mast not be understood that habit formation requiring such 
dexterity is considered easier to originate than modification in 
