40 M;\I A I, ORGANS. 



spcniiMtophorcs li:is been found. ;tii<l tin- hectocoty li/ed arm 

 appears to perform its oilier without subsequent detachment from 

 the animal. Tin- detached heel ocotyle when first discovered in 

 tlie mantle ol' tlu' female was naturally regarded MS a parasitic 

 \vonn: that o!' Argonauta bein^ termed Tri<-/i<-<'/>/i<i/ n.< tn-i-lnlm- 

 tdris by rhiaje and that of Octopus Ili't-lnruhjliix urlo/HH/i* by 

 Cuvier. More recently it was supposed to be the entire male 

 animal of the eephalopod. 



Ill Tremoetopns the third arm <>n tin; ri^'lil side heeoines hec- 

 toeotylixed ; it is then woi'in-lik<' in appearance, with two rows 

 ol' suckers on its ventral surface and an oval appendage at the 

 posterior end. The anterior part of the buck is frin<>vd with a 

 double series of branchial lilainents :2f)0 on eaeh side). IJefween 

 the lilainents are two rows of brown or violet spots. 'Hie suckers 

 (forty on each side: closely resemble, but are much smaller than 

 those of the normal arms. Between the suckers are four or live 

 series of pores, the openings of minute canals passing into the 

 interior. There is an artery and vein on each side. iri\in;j 

 branches to the branchial filaments, while a nerve runs down the 

 centre. The or//,/ .NV/C/- encloses a small but very lon<_: convoluted 

 tube, ending in a muscular sack which contains the spermatozoa. 



The hectocotyle of the Argonaut is very small, only half an 

 inch, with a filiform appendage in front of about eqnal length; 

 it has two rows of alternate suckers, forty-live on either side; 

 but, no branchi;e. 



The Father of Natural History, who was certainly a first -das-* 

 observer, was acquainted with the hectocotyli/ed arm and its 

 functions, but his degenerate >u-cc>sors for many centuries not 

 only misunderstood // but him also. 



In Octopus the hectocotyli/cd arm instead of heinp; much 

 shorter than I lie others, as in Aru'onauta. becomes much longer. 

 It terminates in an oval plate, marked with numerous trans* 

 ridges Mini intervening pits, and this is connected by a muscular 

 fold of skin running alono- the dorsal face of the arm with the 

 webbed base, covering a passage through which the spermato- 

 phores are probably transmitted to the terminal plate. 



It, will be seen in the systematic portion of this work that able 

 observers have in some cases regarded as opposite 86X68 only 



