THE OCTOPUS AND ITS RELATIVES 3 



The following diagram will help to explain the relationship of 

 the Octopus to the rest of the cephalopoda. 



MOLLUSCA. 



Classes. .. Cephalopoda. Gasteropoda. Pteropoda. Brachiopoda. Lamell ibrliidUaU. 



Orders. .. Dibranchiata. __^ Tetrabranchiate. 



Sections. . . Decapoda. OctopodI Nautilida.. Orthoceratid^. Ammonitida^. 



Fmnilies.. Teuthidae. Belemnitidse. Sepiidse. Spii^^. Octopida.. Argonautid^ 

 Genera. ..fiTsquid?: l^Cuttles : xl^T^^p"^ flTPaper Nautilu';^ 



Lohs:o, &c. Sepia, &c. O. vulgaris, &c. Argonauia. 



It will be seen that it may be said to be first cousin to the 

 Argonaut, or " Paper Nautilus," and second cousin to the cuttle 

 and squid. 



The Argonaut branch of the family is in possession of all the 

 house property, which seems to have been entailed on the female 

 line ; for the paper-nautilus is, in fact, a female octopod pro- 

 vided with a shell in which to carry and protect her eggs. 

 Instead of the whole of the eight arms tapering to a point, as in 

 the octopus, two of the dorsal limbs are flattened out at their 

 extremity, and from their membranes she secretes, and, if necessary, 

 repairs the shell, and, by applying them closely to its outer 

 surface on each side, holds herself within it ; for it is not fastened 

 to her body by any attaching muscles/^ 



* In the Appendix to Sir Edward Belcher's "Voyage of the Samarang," 

 Mr. Arthur Adams, the Assistant Surgeon attached to the Expedition, gives 

 some valuable information concerning the Argonaut, numerous specimens of 

 which he had opportunities of capturing in the South Atlantic, and observing. 

 He says :— " There is not the slightest vestige of any muscular attachment 

 This remarkable cephalopod carries about her eggs in a light calcareous nest, 

 which she firmly retains possession of by means of the broad, expanded, delicate 

 membranes of the posterior pair of tentacles. When disturbed or captured, 

 however, she loosens her hold, and, leaving her cradle to its fate, swims away 

 independent of her shell." He adds that '' having once left her shell she has 

 not the ability, nor, perhaps, the sagacity, to re-enter her nest and resume the 

 guardianship of her eggs." From obsei-vations of the breeding habits of other 

 octopods I doubt this. 



B 2 



