CEtSALOPODA. 159 



for a parasitic "worm ; and more recently it lias teen regarded 

 as the spermatophore by some, and as the entire male animal 

 by otber naturalists, under tbe name of hedocotylus. The 

 hcctocotyle of tremodopus is shown in Fig. 3, PI. 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- 

 Dicnts (250 on each side). Between the filaments are two rows 

 of brown or violet spots^ like the pigment cells of the tremodopus. 

 The suckers (40 on each side) closely resemble those of the 

 tremodopus, in miniature. Between the suckers are four or 

 five series of p)or€S, 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 Jiedocotyle of the argonaut was discovered by CJu'aje, who 

 considered it a parasitic worm, and described it under the name 

 oi tricliocephalus acdahularis ; it was again described by Costa,* 

 iVho 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 

 Iranchice; the skin contains numerous 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 metamoriDhosed or hecto- 

 cotijliscd 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 i^erformed. 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. Sc. Kat., 2ncl series, 7, p. 173. 



t Lin. Trans., vol. 20, pt. 1, p. 9 ; and in his own zootomical Berichte, wlieie it ia 

 figured. 

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



