THE MARQUIS DE FOLIN ON THE CiECTDiE. 257 



Avoxild observe that the diameter of the tube is greater at the 

 point to which the septum has to be transferred ; aud it is im- 

 possible to conceive of such a proceeding except on the suppo- 

 sition of a slow movement, in consequence of which the septum 

 advances little by little. But, in this case, specimens would 

 be commonly met with in which the translation was in progress, 

 a circumstance that would be very readily witnessed. Never- 

 theless, we can assert that no specimen of a shell of Caecidse has 

 ever come under our notice in which the slightest evidence of 

 such a proceeding has been apparent, although we have examined 

 many thousands. If it is said that it is only at distant periods 

 aiAd at the time of change of shell that the translation takes 

 place, we should be still wholly unable to comprehend the me- 

 chanical operation by which it is accomplished, which would de- 

 mand such great perfection in the movement by which the sep- 

 tum was displaced in order that it should be brought correctly 

 into the " plane of obliteration," perpendicular to tlie axis, and 

 with the apex invariably situated at the same point near the right 

 side of the shell. In a perfectly smooth tube, how could the 

 animal, without Siny point d'appui, perform such a transference, 

 demanding rigidity and precision in order to obtain always iden- 

 tical results? Such a thing appears to us impossible, aud we 

 should have rejected the supposition, simply relying upon the 

 arguments already adduced, and which appear to us amply suffi- 

 cient to disprove it, if a positive proof in the same direction had 

 not presented itself against the opinion of Mr. Carpenter. "We 

 have lately received from New Providence (Bahamas) some spe- 

 cimens of a new species of Geecum, G.forinosuluin, amongst which 

 is a complete shell of the third stage still attached to that of the 

 second. Having glued it on a piece of glass in order to examine 

 it, and some time afterwards having moistened it for the pur- 

 pose of transferring it to another glass, for which I employed a 

 very delicate pair of forceps, my double Ccecum broke in two 

 under the pressure of the instrument. It was a clean fracture 

 in the "plane of obliteration," and with a perfectly straight cir- 

 cumference. On the glass tablet were now two shells, each 

 furnished with a septum. That of the adult shell was remark- 

 able in its having undergone no apparent abrasion. Consequently, 

 the two septa were placed one on the adolescent and the other on 

 the shell of the third stage, although but a moment before they had 

 both appertained to the same shell. We think that an instance 



