258 
ME. CHAELES S. TOMES ON THE 
To confine the discussion for the present to the Elasmobranch Fishes, Professor Owex, 
as shown in the above quotation, holds that their teeth stop short at a “ papillary ” 
stage equivalent to that supposed by him to exist at an early stage of the formation of 
a human tooth ; while against this we have the opinion of Professor Huxley, that “ the 
process seems to correspond with something more than the first and transitory papillary 
stage of the development of the mammalian teeth.” 
The application of modern methods of microscopic research has rendered it possible 
to obtain sections showing the relation of the various structures over a far larger area 
than was formerly practicable ; and the facts thus brought to light appear to me to be 
of sufficient interest to merit careful description, although in many of the essential 
points I have been anticipated by Professor Huxley, as is shown by the extract here 
subjoined. 
“ In the Skate, as is well known, the young teeth are developed in longitudinal rows 
within a deep fold of the mucous membrane of the mouth, behind the jaw. So far as 
my examinations go, however, I find that this is not a mere simple fold, such as it has 
been described to be, but its two walls behave just in the same manner as those of the 
primitive dental groove in man — that is, they become closely united in lines perpendi- 
cular to the direction of the jaw, so that partitions are formed between every two rows 
of teeth ; transverse partitions again stretch between the separate teeth of each row, but 
these did not appear to me to be complete, terminating by an arcuated border below. 
Each longitudinal canal, therefore, answers to a single elongated mammalian follicle, 
or to that prolongation of the alveolar groove from which the posterior permanent 
molars are formed in man (see Goodsir), only the process does not go so far as in this 
case, the separate capsules remaining imperfect anteriorly and posteriorly. The lateral 
walls of the capsule, however, seem to me to have as much (or as little) 4 organic 
d. Sci. Nat. 1850) gave figures of young mammalian tooth-germs, which were very nearly correct ; hut the more 
precise knowledge which we now possess of the sequence of events in the formation of a tooth-germ is due to 
Prof. Kollikee (Zeitschr. f. wiss. Zool. 1863, and Gewebelehre, 5th edition). 
Kollikee demonstrates that an ingrowth of epithelium (termed hy him “ enamel-germ”), which was after- 
wards destined to become the enamel-organ, was first recognizable before the dentine-pulp- became visible ; and, 
further, that the enamel-germ of a permanent tooth was derived from a part of the enamel-organ of its deci- 
duous predecessor, this constituting the sole genetic relation between the two tooth-germs. Legeos and 
Magitot added (Journ. de l’Anat. et Phys. 1873) an account of the origin of the tooth-germs of the true molars. Of 
fish. Prof. Kollikee in his earlier work (Mikroskopische Anatomie, 1854, B. ii. p. 114) states, agreeing with 
Prof. Owen, that the teeth of Plagiostomes are developed from free papillae, and that they have therefore no 
enamel, never having been enclosed in sacs. This last inference is not confirmed by my own observations, nor 
by those of Heetwig, quoted at a later page. 
Prof. Kollikee goes on to say that, the teeth of all other fish (than Plagiostomes) are developed in sacs, some- 
times enclosed within the jaw, sometimes only in mucous membrane, the successional teeth being developed 
anew from the mucous membrane of the mouth, behind the older teeth. The presence of an enamel-organ 
he considers to depend upon the existence of an enamel-like layer upon the teeth ; in this last respect I have 
arrived at a different conclusion, being convinced that an enamel-organ is of universal occurrence, although the 
degree of its after development does in a great measure depend upon the amount (if any) of enamel to be formed. 
