60 Ray Lankester, on the Tooth in Ziphius Sowerbiensis . 
form, or much elongated, narrow cavities. The dentinal 
tubules of one canal do not anastomose to any large extent 
with those of other neighbouring canals, in many cases a wall 
of opaque globular matter enclosing each. The tubules of 
some of the osteo-dentinal canals are very few in number, 
and have an irregular tortuous distribution, the canal, when 
in section in such cases, resembling a very large multiramose 
bone lacuna. 
Comparison with other teeth . — In no other Cetacean teeth 
is the dentine developed to so small an extent, and the cement 
and osteo-dentine so largely concerned, in forming the mass of 
the tooth. In the large conoid teeth of the cachalot the 
dentine occupies a very much greater space in the tooth, the 
osteo-dentine is sparsely developed, and a certain amount of 
basal pulp-cavity is left, while the cement, though forming 
a thick layer on the tooth, is comparatively small in amount. 
In Hyperoddon the small pointed teeth are stated by Professor 
Owen to be tipped with enamel, which does not appear to be 
the case in Micropteron. In the Porpoises and Grampuses 
the dentine has a large development, and osteo-dentine, when 
present, bears but a very small proportion to it. 
Purpose of the teeth . — The teeth of Micropteron are not worn 
at the crown, and are obviously not used for biting, since they 
are not opposed by any part of the upper jaw. They are said to 
be sexual characteristics, Eschricht considering the toothless 
Delphinus micropterus (Cuvier) to be the female of the bident 
Micropteron Sowerbiensis * These teeth, then, obviously have 
their true function aborted, degraded from the class of “ func- 
tions of animal life ” to that of “ functions of vegetable life 
and with this we may expect a corresponding degradation in 
structure, resulting in the production of a tooth of less 
specialised character, and less differentiated from the rudi- 
mentary structure of a developing tooth. This, I think, can 
be shown to be the case with the tooth described above. 
Cement is not a structure belonging specially to teeth ; it is 
merely bone such as exists throughout the body. Osteo- 
dentine is a less differentiated structure than true dentine, 
being formed by a conversion of the substance of the pulp 
instead of at its periphery, and retaining certain elements of 
the pulp in its canals and cavities ; moreover osteo-dentine is 
developed in many teeth ( e . g. human) only as the result of 
age and decrepitude, or as a pathological product ; in others, 
* The female stranded at Ostend is said to have had “a few” small 
denticles concealed in the anterior part of the lower jaw. It is not at all 
improbable that the male, when young, has many teeth, one only of which on 
each side is developed. 
