1893. NOTES AND COMMENTS. 251 
the microscope, but the threads were of a quite different structure, 
consisting of long cells, almost all of the same form, and, according to 
the author, evidently belonging to a monocotyledon presumably 
Posidonia, numerous rootstocks of which occurred on the beach mixed 
with the pine cones. These long filaments had played the part of a 
thread uniting the smaller débris, which otherwise would probably 
have remained separate. 
Other cases are mentioned in which the Posidonia fibres act in 
this way. Bits of sponge may form a nucleus round which they 
group themselves, while seaweeds may get involved. An example 
exists in M. Bornet’s herbarium, a green alga in the shape of a ball, 
in which the Pos:doma filaments are caught like pins. The latter 
example is comparable with the instances cited by Masters, and 
found in certain small English lakes, of Conferve interlacing and 
forming a ball with the leaves of the larch. 
These recall the so-called aegagropilous algz, which are merely 
species of the green alga Cladophora, detached at an early stage from 
their support, and rolled by currents. As Russell suggests, all sub- 
merged bodies, under certain circumstances, might form similar 
pellets. The pine needle balls from the lakes of the Engadine are 
well-known, and M. Jaccart, of the Lausanne Museum, states that 
in a little creek in the Lake of Geneva, where the water is unceasingly 
disturbed by currents, fine felted pellets may be seen formed by 
shavings from a saw-imill. 
EvoLuTION OF PREMOLAR TEETH. 
Tuat indefatigable worker, Professor W. B. Scott, of Princeton, 
has contributed to the last issue of the Pvoc. Acad. Nat. Sci. 
Philadelpia (1892, pp. 405-444), a very interesting paper on the 
evolution of the premolar teeth of mammals, especially those of the 
Ungulates and their allies. It is clearly shown that premolars start 
as simple cones, and receive their first accression by the addition of a 
smaller cone on the inner side. It is thus evident that the protocone 
in these teeth is external; whereas, according to the general inter- 
pretation, in the true molars it is an internal element. Professor 
Scott is thus led to conclude that in Ungulates like the horse, when 
the upper premolars exactly resemble the molars, the various cusps 
of these two series of teeth are not homologous with one another. 
He, therefore, proposes a new series of terms for the premolar cusps. 
The idea that such precisely similar teeth have a totally different 
origin for their cusps is sufficiently startling to make us anxious to 
ascertain whether the inductions on which the theory rests are well 
founded. Now, at the conclusion of his paper, Professor Scott 
mentions that Herr Rése has recently come to the conclusion that in 
quadritubercular upper molars the cusps have been wrongly identified, 
and that the protocone is, after all,external. If this be so, adds Pro- 
