WOODWARD : INAUGURAL ADDRESS. 253 



Turning next to the form of the animal itself, it cannot be said that 

 any definite line of development is presented, unless, perhaps, in the 

 case of the more specialized Gastropoda, where, with the discarding of 

 the shell, the visceral hump tends to be smoothed down and distributed 

 along the dorsal keel till the true slug-like form is attained. Even 

 this seems to be due to the burrowing habit of the animal rather than 

 indicative of any definite product of development. 



The foot largely modifies in response to individual requirements, 

 whether for locomotory or other purpose. The simple reptant foot 

 becomes a strong sucker-like organ in the Docoglossa, Haliotis, and 

 other rock-frequenting kinds. It assumes the snow-plough outline in 

 Natica, Sigaretus, and other species that search about in loose surface 

 sand for their bivalve prey. It is expanded and functions like 

 a snow-shoe in those of the Bullidae that frequent very soft ooze, 

 while the widely extended pleuropodial ' margins function as fins, 

 enabling the animal to swim {^Hydatina, Gastropteron, etc.). In the 

 pteropods and other oceanic gastropods it is modified into a swimming 

 organ, but in this connection it is interesting to note that, according 

 to Tesch,* the fin of the heteropod is constituted by the extension of 

 the columella muscle through the true foot and its fan-like expansion 

 into the swimming organ. 



In the Pelecypoda the primitive reptant foot of the Nuculidas 

 becomes a leaping organ in Cardium and Tririonia, and converted by 

 successive stages into an efficient digging organ in the burrowers, 

 while it is aborted in fixed forms. 



The Cephalopod foot has made more definite progress. Beginning 

 with the numerous series of weak tentacles in the Nautilus, and 

 presumably also in the fossil predecessors and allies thereof, it 

 culminates in the powerful eight- armed weapon of Polypus. 



The alimentary system does not furnish any particular evidence 

 with respect to our quest of the moment, although, taking the 

 molluscan group as a whole, the radula, which is characteristic of the 

 phylum, does. 



Speaking broadly, the teeth in the older families are numerous and 

 weak. There may be as many as 300 or more teeth in each transverse 

 row in the Khipidoglossa. Our late Secretary, Mr. Martin F. 

 Woodward, in his careful and most excellent monograph on " The 

 Anatomy of Pleurotomaria Beyrichii,'''' discussed the question of the 

 radula, and gave reasons ^ that will hardlj- be disputed for thinking it 

 represents the most primitive type among all existing Gastropoda, 

 and, further, that it was derived from one in which all the teeth in 

 a transverse row were similar. In Pleurotomaria, although all the 

 various specialized tooth areas merge into one another, five tracts on 



The term ' parapodia ' adopted by some authorities has already long been in use, in 

 a very different sense, for quite other animals ; nor does ' pteropodia,' proposed 

 by von Jhering, seem quite appropriate. Garstang's alternative term, therefore, 

 seems preferable. 



Siboga Expeditie, vol. li, p. 104. 



Quart. Journ. Micro. Sci., n.s., vol. xliv, p. 255. 



