PRESIDENTIAL ADDRESS. o21 
which had become detached and found its way thither, bearing with it the 
fertilising element—a procedure quite unique, not only among the Cephalopoda, 
but also among the Mollusea, if not in the whole animal kingdom, The gist of 
Steenstrup’s discovery was that, although the separation of an arm was peculiar 
to very few forms, the modification of one or other of the arms for reproductive 
purposes was of common occurrence among the Cephalopoda ; and, furthermore, 
that the situation of the particular arm, which was so modified, varied with the 
systematic position of the genus in question, and was constant through the main 
divisions of the class. To this less extensive modification of the arm he gave the 
name ‘ hectocotylisation,’ and expressed his conclusions in the following table :— 
“OCTOPODA f 
left 
Argonauta f 
Philonexide 5 (Philonexis) } third 
Tremoctopus right J 
Octopide { me ba, third right arm hectocotylised (feminz monandrz ?) 
[arm a Hectocotylus (feminz polyan- 
dree !) 
DECAPODA. 
Rossia | first left aaa (with the right one, only in the middle) 
Sepiola } hectocotylised | (alone in its whole length) 
Sepia (at the base) 
Myopside Seoicteuthio | fourth left arm } (at the apex) 
Loligo { hectocotylised | (at the apex) 
Loliolus (in its whole length) 
Ommatostrephes i 
Oigopside Onychoteuthis no hectocotylised arm hitherto observed.’ 
| Loliyopsis J 
Stimulated by this discovery, other zoologists examined the Cephalopoda in 
their possession, and described the modifications in various genera, and now it is 
universally recognised that no definition of a Cephalopod is complete which does 
not include a description of the position and form of the hectocotylised arm. 
The descriptive anatomy of this organ is fairly well known. Out of twenty-two 
families, which may be regarded as well established, its structure is known in a 
number of genera in no fewer than twelve, whilst of the remaining ten it has been 
more or less conclusively shown that in seven no modification of the arm takes 
place, so that there are only three families in which we are still without any 
information regarding it. 
Our knowledge of the physiology of the apparatus has not, however, advanced 
with anything like the same rapidity. Even in the case of those forms where a 
true hectocotylusis found (Argonauta, Tremoctopus, and Ocythoé) it is not known for 
certain whether the fertilising arm is deposited by the male in the mantle-cavity 
of the female (as I think is most probable), or whether (as is stated by some 
writers) the arm breaks off when mature and finds its own way to its destination. 
This much is certain, that for some time after its detachment it possesses the power 
of independent movement. 
As regards the function of the modified but not detachable arm, we have the 
important and interesting observations of Racovitza (37) made at Roscoff and 
Banyuls on the genera Polypus (Octopus) and Sepiola. It appears that in the 
first of these forms the extremity of the hectocotylised arm of the male is intro- 
duced into the mantle-cavity of the female, both individuals resting on the sea- 
bottom and at some distance from each other (about 25 cm. in the case of a male 
measuring 1:25 m. in total length). Although after an encounter the female 
appeared to flee the embraces of the male, and although the males, when two 
were placed in the same tank, fought with each other, there was no sign of any 
combat between the sexes as was described by Kollmann (28). In Sepiola (36) 
the female is roughly seized by the male, and held with the ventral surface 
uppermost ; the two dorsal arms are introduced into the mantle-cavity, whilst the 
other three pairs hold the female firmly. ‘The efforts of the male are directed to 
