328 Mr. W. Clark on the Animal o/Dentalium Tarentinum. 



duction, and I think from various considerations that this ani- 

 mal 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 glary 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 curious and anomalous structure of 

 this moUuscum, and the multitude of interesting characters at- 

 tached to it, exhibit such modifications of the organs of the ty- 

 pical 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, malacologists may be in- 

 duced to think that it will appropriately form one of the first, if 

 not the first link, in the chain of the Gasteropoda. The symme- 

 trical subventral position of the branchise, 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 Con- 

 chiferse ; whilst by its oesophageal cerebral ganglions and com- 

 pleteness 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 configuration 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 various points the progress of advancement, and the 

 ameliorations nature has so beneficently efi'ected in its animality. 



I have only seen one live specimen of the Dentalium entalis : 

 the organs have the same characters as those of the present spe- 

 cies, but it is very distinct ; the colour is snow-white, and on com- 

 parison of two shells of the same size, the Dentalium entalis will 

 be found much more slender ; the branchiae are also of a paler 

 green, more scanty, thin and delicate. 



I had written thus far when I received from Paris M. Deshaycs's 

 memoir on the Dentalia, which I had not seen for twenty years, 

 and its contents had nearly passed from my memory ; on looking 

 it over I find that the differences between that gentleman and 

 myself are more important than I was aware of, but I am not 

 inclined to abandon my own views. I am also glad to find that 

 I am enabled to fill up many gaps as regards the functions and 

 habitudes of these animals. 



This gentleman, in stating the anus in Dentalium to be pos- 



