572 CEPHALOPODA. 



and consequently the keel. The application of these membranes is 

 direct, and without any puckering or irregularity whatever, the lower 

 part of the two large arms being completely stretched, so as to form a 

 kind of bridge over the cavity left between the back of the mollusk and 

 the retreating portion of the spire. When the mollusk contracts itself, 

 it frequently draws in more or less completely its large arms and their 

 membranes, so as partially to uncover the shell in front, as is repre- 

 sented in the figure (fig. 286). 



(1533.) There is little doubt that the vela of the Argonaut, which 

 thus envelope its abode, are the organs employed in constructing the 

 brittle fabrics, and the agents whereby fracture and wounds in the 

 shell are repaired and filled up. 



(1534.) The positive experiments of Madame Power* leave no doubt 

 upon the subject ; for not only did that lady, by rearing young Argo- 

 nauts from the egg, watch the first appearance and earliest growth of 

 the shell, but, by breaking the testaceous covering of adult specimens, 

 she found that they could readily repair the damage inflicted. Being 

 desirous of observing the manner in which this operation was accom- 

 plished, the lady to whom science is indebted for these interesting 

 researches examined an individual on the day after its shell had been 

 intentionally broken, and found that the aperture was already covered 

 by a thin glutinous lamella, which, although as yet as delicate as a 

 cobweb, united the margins of the fracture. The next day the lamella 

 had become thickened to a certain degree and more opake; till at 

 length, at the end of ten or twelve days, the new piece had become 

 quite calcareous. Madame Power is likewise certain that, while in the 

 act of mending the fractures, the Argonaut applied its vela to the exte- 

 rior of the shell, and wrinkled them upon it ; whence they may naturally 

 be regarded as being the source from which the glutinous secretion that 

 finally became hardened into shell proceeded. 



(1535.) In order to understand the manner in which the remarkably- 

 constructed camerated shells, such as those of Nautilus, are produced, 

 it is not necessary to imagine any deviation from the simple mode of 

 procedure adopted in all the cases we have as yet considered. The 

 continual elongation of the spiral cone is, as is evident from the lines of 

 growth visible upon its outer surface, effected by the addition of suc- 

 cessive layers to the margin 6f the aperture of the last-formed chamber, 

 wherein the animal resides ; and as the production of the calcareous 

 secretion whereby the shell is enlarged is most rapidly effected upon 

 that side of the body where the funnel (fig. 284, {) is situated, the 

 gradually- expanding shell naturally revolves around an excentric axis. 

 While the growth of the shell continues, the animal is constantly 

 advancing forwards, and thus leaves the first-formed portions of the 



* Magazine of Natural History, April 1839, " Observations on the Poulpe of the 

 Argonaut," by Madame Jeannette Power. 



