424 PROF. OWEN ON THE ARGONAUT. 



" Mr. Owen stated that the correspondence in the progressive increase of 

 inhabitant and shell, though not strictly conformable, was so close as to 

 present, in his opinion, an insurmountable objection to the parasitic theory. 

 In every instance the inhabitant of a larger shell weighed more than that 

 of a smaller one, even where the difference in the weight of the shell was 

 but half a grain ; while the few irregularities observed in the progressive 

 increase of the two could in each case be accounted for, either by the en- 

 largement of the ovarium, which added to the weight, without a propor- 

 tional increase to the superficies of the individual ; or, on the other hand, 

 to a more rapid increase in the thickness of the shell at the earlier periods 

 of its growth, or to a greater development of the angular processes of the 

 mouth of the shell, as an individual peculiarity. In a collection of young 

 parasitic hermit-crabs (Paguri), the smaller specimens are commonly seen 

 in shells of various species, and frequently very disproportionate bulk ; the 

 contrary is the case in the young of the argonaut. ' Now these young ce- 

 phalopods (Mr. Owen observed) grow, like the rest of the class, with great 

 rapidity ; the differences in the size of many of the young argonauts in 

 question corresponded with differences of age of a few days at the utmost;' 

 so that, if the accuracy of the above observations made by Mr. Owen on two 

 series of two distinct species of argonaut, be admitted, 1 ' a naturalist enter- 

 taining the parasitic theory, must be compelled to suppose that the young 

 Ocythbeov cephalopodis engaged ina perpetual warfare with the hypothetical 

 nucleo-branchiate constructor of the argonaut-shell, which shell, to produce 

 the correspondences above described, the young Ocythoe must change two 

 or three times a week, if not every day. And nevertheless, although each 

 prolific cephalopod of the argonaut sends into the world hundreds of little 

 ones that must be so accommodated, and although, on the parasitical hy- 

 pothesis, hundreds of the hypothetical nucleo-branchiate constructors of the 

 argonaut-shell ought to swarm about the port of Messina, where Madame 

 Power obtained the specimens with which she stocked her molluscous viva- 

 rium, and notwithstanding that M. de Blainville has called the special at- 

 tention of naturalist-collectors to the hypothetical true constructor of the 

 argonaut-shell, as a chief desideratum in Malacology ; and lastly, notwith- 

 standing this hypothetical nucleo-branchiate mollusc ought, on M. de 

 Blainville's theory, to be nearly allied to the Atlanta and Carinaria, and 

 therefore a floating pelagic species, generally to be met with on the surface 

 of the ocean ; — yet had it still evaded the observation of the numerous ac- 

 tive collectors engaged in exploring the zoological riches of the Mediter- 

 ranean in different parts of its coasts.' 



" It is in vain to repeat, with reference to the non-discovery of any other 

 inhabitant of the argonaut than the cephalopod, — ' Ce que ne peut etre 

 range au nombre des argumens, parceque ce qui n'as pas eu lieu jusqu' a 

 un moment determine, peut se montrer le moment suivant; ' that ' what is 

 a fact at the present moment, viz. the non-discovery of the hypothetical 

 true constructor of the argonaut, may be no longer a fact at the moment 

 after.' Such an observation could only possess argumentative force in the 

 absence of other facts showing the high degree of improbability that a float- 

 ing pteropod or heteropod, sufficiently abundant to have supplied all the 

 argonauts of the Mediterranean with their shells, could have escaped ob- 

 servation.' 



1 They accord with the statement of Poli, and with the observations of 

 M. Prevost, founded on a suite of specimens of the argonaut from the size 

 of one and two inches to three or four inches. These are quoted byM. de 

 Blainville in his memoir of 1837 (p. 10), but without the deductions which 

 I have drawn from the same facts. 



