CEPHALOPODA. 150 



for a parasitic worm ; and more recently it lias been regarded, 

 as tlie 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, PI. I. The body 

 is worm-like, with two rows of suckers on the yentral 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 vein 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 name 

 oi trichocephalus acetabularis ; it was again described by Costa,* 

 who regarded it as "a spermatophore of singular shape ; " and 

 lastly by Dr. Kolliker.f 



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 

 hranchice; the skin contains numerQus changeable spots of red 

 or violet, like that of the argonaut. | (Kolliker.) 



It would seem strange how former observers 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 have 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. Fc. Nat., 2nd series, 7, p. 173. 



t I^in- Trans., vol. 20, pt. 1, p. 9 ; and in Ilia own zootomical Berichte, where it is 

 figured. 

 X An. Sc. Nat,, 2nd series, vol. 16, p. 185. 



