110 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
other ; (3) alternation of generations is “ a fragmentation of the indi- 
vidual,” a division of the specific individuality into two stages ; (4) meta- 
morphosis or metahole is the result of a diminished vitality in ontogeny, 
of a period of local asphyxia, and is associated with phenomena of 
necrobiosis ; (5) what Beard regards as an alternation of generations in 
Vertebrata seems to Houssay rather a metabole. It may be noted that 
this paper does not take account of Beard’s paper summarised above. 
Development of Teeth in Perameles.* — Prof. J. T. Wilson and 
Mr. J. P. Hill base on their observations on the development of the 
teeth of this Marsupial a simpler view of the dentition of these animals 
than that now in vogue. 
They regard the permanent teeth of Marsupials as the homologues 
of the permanent or replacing teeth of other Mammals. They find the 
deciduous premolar to be a true milk-tooth, while the so-called prelacteal 
teeth are in reality milk-teeth which have undergone reduction. The 
lingually situated downgrowths of the dental lamina by the sides of the 
developing teeth are not rudimentary enamel-germs. They are merely 
portions of a quite indifferent “ residual dental lamina ” ; the swelling of 
the distal portion exhibits no differentiation which is really characteristic 
of actual enamel-organs. 
Experiments on Growth of Blastoderm of Chick. + — Mr. R. Assheton 
set himself to test by actual experiment Duval’s theory of the formation 
of the primitive streak, and to try and determine experimentally whether 
the whole or only part of the actual embryo is developed by the activity 
of the primitive streak. 
The result of the first set of experiments seemed to be that the 
primitive streak is not formed from the posterior edge of the blasto- 
derm, as Duval maintains. 
It further seems clear that all the parts of the chick in front of 
the first pair of mesoblastic somites (that is, the heart, brain, olfactory, 
optic, and auditory organs and foregut) are developed from that portion 
of the blastoderm which lies anterior to its centre, while all the rest of 
the embryo is formed by the activity of the primitive streak area. 
Proportions of Yolk, Albumen, and Shell.J — Hr. R. W. Bauer 
continues his painstaking estimation of the proportionate weights of 
yolk, albumen, and shell in birds’ eggs. In Columba romana, the yolk 
weighed 4*967 gr., the albumen 15*648 gr., the shell 3*355 gr. ; or, in 
percentages, 20*72, 65*29, and 13*99 respectively. 
Blastopore of Chelonia.§ — Prof. K. Mitsukuri, in this part of his 
contributions to the embryology of Reptiles, treats of the “ fate of the 
blastopore, the relations of the primitive streak, and the formation of 
the posterior end of the embryo in Chelonia, together with remarks on 
the nature of mesoblastic ova in Vertebrates.” 
The author has made a study of the surface changes and of what 
may be seen in sections of Chelonia caouana , Clemmys jajoonica, and 
Trionyx japonicus. He is led by his investigations to suggest a reclassi- 
fication of the eggs of Vertebrates : — 
* Quart. Journ. Micr. Sci., xxxix. (1897) pp. 427-588 (8 pis.). 
t Proc. Roy. Soc. Lond., Ixi. (1896) pp. 349-56 (5 figs.). 
% Biol. Centralbl., xvi. (1896) p. 848. 
§ Journ. Coll. Sci. Imp. Univ. Japan, x. (1896) pp. 1-118 (11 pis.). 
