888 
ME. S. J. A. SiVETEE ON THE STEUCTUEE AND 
fied specimen of what appears to be a piece of shell or alveolus. I am quite unacquainted 
with any appearances in the Echinus-tooth resembling this figure. 
Professor Quekett in 1854 published his lectures on histology*. He there simply 
alludes to the mature structure of the tooth without reference to its general anatomy or 
mode of development. 
Eespecting the structure of the compact tissue, Professor Quekett remarks, at page 
235, that the teeth “contain numerous branching tubuli very like those of dentine; 
many of the tubuli are so much dilated at certain points as to form lacunee, or bone-cells, 
but in others the branches are extremely minute, and run in parallel lines precisely like 
the tubuli of dentine.” This account is quite correct, but it should be observed that the 
dentine-like appearance is displayed by transverse section; the bone-like appearance by 
vertical section. 
Professor Quekett further observes that he has failed to discover any walls to the 
tubular structure of the Echinus-tooth. 
Dr. Cakpektee, in his work on the micro scope f, published in 1856, adds no further 
information respecting the structure of the Echinus-tooth ; but, as qualifying the imphed 
opinion of Professor Quekett, he remarks that he “ is disposed to think that the struc- 
ture of the teeth is essentially the same as that of the shell, save in the interspaces of 
the network being much narrower; and that the appearance of tubuli (in which 
Mr. Quekett has not been able to make out distinct walls) is due merely to the elonga- 
tion of these interspaces.” — Page 519. 
Professor Williamson, in December 1856, published a valuable and original paper;]: on 
the anatomy and structure of the Echinus-tooth in the ‘British Journal of Dental Science; ’ 
but Bom its appearing in an obscure professional periodical, it has unfortunately been 
lost to science nearly altogether ; the author of this memoir, indeed, only becoming acci- 
dentally aware of its existence more than a year after its publication. 
Professor Willia:mson’s paper is one of great excellence. He does not, however, 
appear to have been aware how far he had been anticipated by Yalentin, especially in 
the illustrations of his monograph, to which, indeed, he makes no allusion. This paper 
contains a good account of the minute structure of the mature tooth, fuller and more 
particular than that of Professor Quekett ; but its author does not seem to have suc- 
ceeded in associating in the fully-formed organ the previously seen elementary parts 
with their then position, or the method in which they build up this curious and com- 
plicated fabric. He observes, “ It is wholly impossible by verbal descriptions to convey 
any idea of the intricate arrangements of plates and rods which compose this singular 
structure.” The difficulty, however, is not in describing but in making out what that 
arrangement is. 
* Lectures on Histology. By J. Quekett. London, 1854. 
t The Microscope and its Eevelations. London, 1856. 
J “ On the Histology of Dental and Allied Dermal Tissues of Vertebrate and Invertebrate Animals,” by 
"W. C. "WiLLiAMSOX, E.E.S., in the ‘British Journal of Dental Science.’ London, 1856, page 163. 
