ANATOMY AND LIFE HISTORY OF MOLLUSCA. 107 



the World. As we descend in the scale of life, however, this 

 character becomes less marked, and amongst the Mollusca, though 

 still evident, it is not strikingly apparent. 



If we examine into the question, as to what the peculiar features 

 of the Australian Molluscan region are, we find them to consist : — • 



1. In the possession of a few remarkable genera which are not 

 found in other parts of the World. These contain but few species 

 for the most parfc. 



2. In the possession of abnormal forms of genera which are 

 found elsewhere. 



3. In possessing living representatives of extinct fossil forms 

 of Molluscan life, which have played an important part in the 

 earth's former history. Australia has in several other sub-kingdoms 

 remarkable instances of these " survivals " which may be said to 

 be the specialty of its Zoology. 



4. In the singular and unaccountable possession of genera and 

 species, which are only known in provinces a great distance apart. 



5. In the possession of extraordinary organs in a few instances, 

 such as have been only known to a limited extent amongst 

 Mollusca generally, though not confined to Australia. This 

 peculiarity will be the subject of the inquiries and experiments 

 recorded in this paper. It should, however, be borne in mind, 

 that these organs may become less and less extraordinary as the 

 animals elsewhere are more carefully and extensively studied. 



Having pointed out the peculiarities, it must be added that 

 they only affect the anatomy and life-history of Australian 

 Mollusca to a very slight extent : that is to say, the dissections 

 and life observations reveal nothing, or scarcely anything different 

 from what is found amongst Mollusca elsewhere. Thus the 

 dissection of our fresh-water Unio, or our salt-water oyster and 

 sea mussel, show that they are, in all but the most trifling 

 particulars, identical with similar animals in Europe. Or, again, 

 a careful examination of the animals of our marine periwinkle 

 or common garden slugs or snails gives us the same organs, disposed 

 in the same manner as the familiar Mollusca of the same kind 

 elsewhere. Our Unio has the same peculiarities of the cardiac 

 region, with the outer gill distended with Glochidia or young 

 Mollusks whose initiatory life-history is there unfolded before us. 

 The buccal mass of our snails has the same arrangement of the 

 protractor and retractor muscles ; the Radula is of the same type, 

 and Ave find precisely similar distinctions between the dental 

 formula of the various genera. In the course of some years 

 observation, anatomical and microscopical, and in observations on 

 the habits of species, naturalists have come to the conclusion that 

 nothing unusual in these directions is revealed to the observer in 

 Australia. If any lines of investigation are open to the anatomist, 



