38 



further extent, and Mr. Owen had not only done so in reference to 

 their relative size, but had also -weighed the shell and its inhabitant 

 separately of each specimen, from the smallest up to that in which 

 the ova \vere fully developed in the ovarium. The following tabular 

 view was given of the weights and measurements of ten of the 

 alternate specimens in this series. 



Mr. Owen stated, that the correspondence in the progressive in- 

 crease 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 enlargement of 

 the ovarium, which added to the weight, without a proportional in- 

 crease 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 peculiaritj'. In 

 a collection of young parasitic Hermit-crabs {Paguri) the smaller 

 specimens are commonly seen in shells of various species, and fre- 

 quently very disproportionate bulk ; the contrary is the case in the 

 jj^oung of the Argonaut. " Now these young Cephalopods (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 ques- 

 tion corresponded with differences of age of a few days at the ut- 



* In each case the Cephalopod was removed frord the shell, and both 

 were placed on blotting-paper, to absorb the superfluous liquor; due care 

 was taken to weigh each specimen under conditions as precisely similar as 

 possible. 



f The disproportionate ratio in the increase of the shell B arises from 

 the additional portion of the shell being thicker and heavier in propor- 

 tion to the previously-formed part, than in the subsequent periods of 

 growth, so that the increase of weight is in a greater ratio than the increase 

 of size. 



X Clusters of ovisacs were conspicuous in D to the naked eye in the 

 ovarram, which had already begun to expand under the sexual stimulus. 



§ The ovarium has now begun rapidly to enlarge. 



II This admeasurement was taken in a straight line, traversing the longest 

 diameter of the shell ;- it was found impracticable to give any constant 

 admeasurement of the Cephalopod, in consequence of the varying state of 

 contraction and form of its soft and changeable body. 



