Tae MicroscopicaL News 
AND 
NORTHERN MICROSCOPIST. 
No. 40. APRIT: 1884. 
THE FORMS, ORIGIN, AND DEVELOPMENT 
OF THim TE EAL: 
By Parsons SHaw, D.D.S., (U.S.A.) 
HE predecessors and the equivalents—the ancestral forms and 
the analogues—of the structures we know as the teeth, are 
found among the earliest products of the animal economy. As 
soon as animals begin to be predatory, they must have some 
means of capturing their prey. Hence we find hard organs of a 
chitinous, horny, or other substance at the extremities of the 
appendages and around the mouths of most creatures, which are 
ingeniously contrived for seizing, holding, and dividing the prey. 
It is a great step from a beetle to a tiger, but there is much 
similarity in the forms and uses of their claws ; and when a chetah 
plants his canine teeth in the neck of an antelope and sucks its 
blood, he repeats what a water-scorpion does when it grasps its 
prey, and then, by means of its rostrum, feeds upon the juices. 
The first office, therefore, of these hard appendages is prehensile ; 
and that office they retain, in a greater or less degree, to the end. 
In many of the shell fishes we find structures on their appendages 
identical in shape and use to those of insects. In the mollusca we 
begin to discover an approach to the arrangement we call teeth in 
the higher forms of life, for we find in the buccal masses of these 
animals what are termed odontophores. These are membranous 
plates, upon which are arranged vast numbers of minute cones 
and hooklets, forming a strap-like masticating organ. These odon- 
tophores are protruded from the mouth to scrape up the food, 
Those who keep aquariums will have noticed how soon a snail will 
clean off the conferve from the glass. This is done by its 
odontophore. ‘This structure is also sometimes used to remove the 
* A paper read before the Manchester Microscopical Society. 
VOL, IV. 
