602 



CEPHALOPODA. 



(fig. 299, l, 2) is of very small size as compared with the female, being not 

 more than an inch in length, and has no shell ; moreover the upper pair 

 of arms are not, as in the female (fig. 283), expanded into velae, but are 



Fig. 300. 



1. Sacculus of Argonaut laid open, showing the abnormal arm (^Hectocotylus) folded up in 

 its interior ; magnified two diameters. 2. A portion of the Hectocotyliform arm, still further 

 magnified: a, the sacculus laid open; 6, the arm, showing the commencement of the "lash," 

 and also the suckers, nervous ganglia, &c. 



pointed. The sac above alluded to, on being opened, is invariably found 

 to contain a solitary Hectocotylus, the dilated portion of which is attached 

 at its base, whilst the rest of this remarkable organ is free and rolled up 

 towards that side upon which the suckers are situated ; but as soon as 

 the sac is opened, or when it is ruptured by the movements of the con- 

 tained Hectocotylus, the latter unfolds itself (fig. 301, a), assuming so 

 exactly the appearance of a parasitic animal that the mistake committed 

 by Cuvier is by no means surprising. The Argonaut itself possesses a 

 well- developed testis, according in its structure with that of ordinary 

 Cuttle-fishes, and which contains spermatozoids in different stages of 

 development; but its excretory duct terminates in the Hectocotylus, 

 which is evidently nothing more than one of the arms of the Argonaut 

 thus strangely developed. But, what is stranger still, this arm, arrived 

 at maturity, detaches itself from the Argonaut, and from that moment 

 enjoys an independent existence. It lives adherent to a female Argonaut, 

 which it impregnates by a real coitus ; so that in this respect, as well as 

 by its movements, and by the length of its life after its detachment, it 

 might be mistaken for a complete male animal. Still it cannot be re- 

 garded as an independent being, seeing that it has no alimentary appa- 

 ratus ; neither is it the organ whereby the seminal fluid is produced, but 

 simply a vehicle whereby the male secretion is transported. Well 

 indeed does it deserve the epithet bestowed upon it by Cuvier, who, 

 ignorant of its real nature, pronounced it " un ver bien extraordinaire !" 

 (1609.) From the pouch of Needham a short canal leads to the penis 

 (h), a short, hollow, muscular tube, through which the fecundating fluid 

 is expelled. 



