Dr. J. E. Gray on the Structure of Humphreyia. 19 



gillum in general ; most probably the latter, as in his work pub- 

 lished since the paper, he still places the species in the subgenus 

 Foegia of the same genus. 



Some persons, to whom I have stated my idea of the struc- 

 ture of Humphreyia, have suggested that the tube o^ Aspergillum 

 might be developed in a similar manner, after the animal had 

 attained its full size in the sand, without any tube; and they 

 explain in this way why the tube of several species of IVarnea is 

 nearly cylindrical ; but the tubes of many species are clavate, 

 small at the siphonal and large at the front end. I cannot 

 agree to this theory, as I do not know of any mollusk that lives 

 sunk in the sand, and then developes a tube; while, on the 

 other hand, Teredo, Gastrochana, and other conchifers which 

 live in tubes, form them as soon as they are hatclied, and the 

 tube may be observed increasing in length and diameter as the 

 animal grows, — sometimes even, as in Furcella, forming a septum 

 across its base, which is removed when the animal again desires 

 to enlarge its habitation. It is further to be observed, that 

 though the tube of some Gastrochame and Teredines is clavate, 

 yet in other Teredines it is nearly cylindrical ; and in all these 

 the siphonal end is modified, sometimes elongated, or even 

 reproduced during the life of the mollusk, as in Aspergillum. 

 A good account of the manner in which Gastrochcena enlarges 

 its more or less exposed, irregular clavate, or retort-like tube, 

 would be an interesting communication, as it is difficult to 

 understand how the small closed chamber of the young shell is 

 altered to the larger chamber of the full-grown individual, unless 

 the animal absorbs and re- deposits the base of the tube after it 

 has increased its size, as the animal of Furcella is shown to do, 

 in my paper on the development of that genus in the * Annals ' 

 for April 1858, p. 295; but I have not observed any specimen 

 which justified my coming to that conclusion. 



We have been long aware that the valves of Aspergillum and 

 Clavagella are, when the animals reach the adult size, soldered 

 into the tube in which they live, which caused them to be for- 

 merly regarded as univalve, and arranged witla the Serpula ; 

 and the exterior appearance of Humphreyia would justify such 

 a position in any cabinet. 



It appears to me that the anomalous structure of Mulleria 

 more nearly resembles that of this shell than any other I know ; 

 for, in both, the animal is hatched with two symmetrical valves, 

 which become united together, and are prolonged behind into a 

 tube. But there the similarity ends ; for in Mulleria the tube 

 is expanded into two lamina? or valves, one of which is at- 

 tached to a rock, the upper lamina breaks off in an irre- 

 gular manner from the end of the tube, and the body of the 



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