234 DENTALIAD^E. 



renders the discrimination of organs of this character a matter 

 of some difficulty. I have not discovered any exserted organs 

 of reproduction, and I think from various considerations that 

 this animal is an hermaphrodite, but without congression. 

 Under the microscope, in the midst of the general mass, 

 several small egg-shaped globules, having at one of the axes a 

 minute, apparently tubular filament filled with a glairy fluid, 

 may be seen in some individuals, but not in all, as I have 

 sometimes searched in vain for them ; these may be the virile 

 fecundating organs, which are perhaps only apparent at certain 

 stages of gestation. 



I have extended these observations to an unusual and 

 almost inconvenient length : the carious and anomalous 

 structure of this mollusc, and the multitude of interesting 

 characters attached to it, exhibit such modifications of the 

 organs of the typical Gasteropoda as appear to give it a claim 

 to be considered as the point of transition from the Bivalve 

 Mollusca to the great change in figure and faculties which 

 nature has produced in the superior developments of the 

 Gasteropoda ; and perhaps, from a review of this account of 

 these organs, rnalacologists may be induced to think that it 

 will appropriately form one of the first, if not the first link, in 

 the chain of the Gasteropoda. The symmetrical subventral 

 position of the branchiae, the posterior flow of water to them, 

 and the resemblance of the foot to that of some of the 

 Bivalves, combined with the similar character of its action, 

 appear in a striking manner to show its connection with the 

 Conchifera ; whilst by its ossophageal cerebral ganglions and 

 completeness of the circulation, it has established its claims as 

 a Gasteropod. There are also traces of alliance with some of 

 the inferior classes : the red blood and vermiform configura- 

 tion of the posterior part of the animal show some of the 

 characters of the Annelides; but though we acknowledge 

 these sources of its origin, we cannot fail to see how clearly 

 the animal of Dentalium displays at varioiis points the progress 

 of advancement, and the ameliorations nature has so bene- 

 ficentlv effected in its animalitv. 



