, CEPHALOPODA: 159 
for a parasitic worm; and more recently it has been regarded © 
as the spermatophore by some, and as the entire male animal 
by other naturalists, under the name of hectocotylus. The 
hectocotyle of tremoctopus is shown in Fig. 3, Pl. I. The body 
is worm-like, with two rows of suckers on the ventral surface, 
and an oval appendage at the posterior end. The anterior part 
of the back is fringed with a double series of branchial fila- 
ments (250 on each side). Between the filaments are two rows 
of brown or violet spots, like the pigment cells of the tremoctopus. 
The suckers (40 on each side) closely resemble those of the 
tremoctopus, in miniature. Between the suckers are four or 
five series of pores, the openings of minute canals, passing into 
the interior part of the body. There is an artery and yein on 
each side, giving branches to the branchial filaments, while 
a nerve runs down the centre. The oval sac encloses a small but 
very long convoluted tube, ending in a muscular sac containing 
spermatozoa. 
The hectocotyle of the argonaut was discovered by Chiaje, who 
considered it a parasitic worm, and described it under the nam» 
of trichocephalus acetabularis ; it was again described by Costa,* 
who regarded it as ‘‘a spermatophore of singular shape;”’ and 
lastly by Dr. Kolliker.t 
It is similar in form to the others, but is only seven lines in 
length, and has-a filiform appendage in front, six lines long. 
It has two rows of alternate suckers, 45 on each side; but no 
branchie ; the skin contains numerous changeable spots of red 
or violet, like that of the argonaut.{ (Kolliker.) 
It would seem strange how former obseryers could have 
overlooked so marked a feature as the metamorphosed or hecto- 
cotylised arm of cuttle fishes. Aristotle not only gives a clear 
description of the peculiarity, but even shows that he was aware 
of the function the arm performed. Subsequent writers appear 
to haye misunderstood Aristotle; at any rate they refer to the 
colourless arm as a monstrosity, or in some cases they have 
used it as one of the distinctive characters of a species. There 
are numerous instances in which the male has formed one, and 
the female another species in the naturalist’s catalogue. Now 
that the hectocotylus is known to be only a portion of the male, 
their relation is more clearly seen. They present an analogous 
phenomenon to what occurs in some species of spiders, in which 
* An, Sc. Nat., 2nd series, 7, p. 173. 
} Lin. Trans., vol. 20, pt. 1, p. 9; and in his own zootomical Berichte, where it is 
figured. 
t An, Sc. Nat., 2nd series, vol. 16, p. 180, 
