346 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The formation of the mesoblast commences at the posterior end of the 
embryonic area, and not at the anterior, as in the hedgehog. 
The notochord is formed entirely from the primitive hypoblast, to 
which it last remains adherent at the dorsal end of the bucco- pharyngeal 
membrane and the anterior end of the primitive streak ; there is no 
cephalic process (“ Kopffortsatz ”) of the primitive streak. 
The author next compares the ova of the rat and mouse with those 
of other Mammals and those of lower Vertebrates. He finds that there 
is no essential difference between the ova of Mammals and those of other 
Vertebrates. They do not consist in the early stages of an epiblastic 
vesicle containing an inner mass of epiblast and hypoblast, but of a large 
hypoblastic mass which supports a small epiblastic disc. The ova of 
Mammals, in fact, present all the characteristic features of comparatively 
large-yolked ova. 
With regard to the formation of the amnion and its relation to 
inversion, Dr. Robinson states that there is no pro-amnion in the rat or 
mouse. Pro-amnion formation and “ inversion ” are distinct processes, 
and “ inversion ” is not precocious pro-amnion formation. The whole 
of the amnion is formed from the tail-fold. The coelom commences to 
be formed bilaterally and in the embryonic area ; the pericardial coelom 
is an extension of the embryonic coelom from behind forwards, and it 
does not communicate with the anterior portion of the extra-embryonic 
coelom. 
Tail of Human Embryos.* — Dr. F. Keibel finds that the tail-liko 
caudal process of young human embryos (between 4 - 2 and 11 *5 mm.) is 
a true segmented tail. In the youngest stage observed three segments 
were seen, and, later on, six could be counted. The nervous system of 
this tail is much better developed in the embryo than in the adult. The 
medullary tube extends as far as the tip of the tail, where it fuses with 
the notochord, enteron, and mesoderm. Four spinal ganglia and two 
spinal nerves could be made out with certainty. 
Embryology of Dentition of Marsupials.! — Prof. W. Kiikenthal has 
made the important discovery of a milk-dentition in Didelphys ; this 
appears to overthrow the generalization that only one tooth in Marsupials 
undergoes successional change, and indicates that the Mammalia were 
primitively diphyodont, and that the milk-dentition is not, as some have 
supposed, a secondary development. 
Development of Apteryx.* — In his memoir on the development of 
Apteryx , Prof. T. Jeffery Parker proposes the following new terms : — 
Chondrite, an independent cartilaginous element or centre of chondri- 
fication. 
Osteite, an independent element or centre of ossification. 
Centrochondrite, cartilaginous, Centr osteite, bony, elements of a ver- 
tebral body. 
Neurochondrite, cartilaginous, Neurosteite, bony, elements of a neural 
arch. 
* Anat. Anzeiir., vi. (1891) pp. 679-5 (2 figs.). 
t Tom. cit., pp. 658-66; translated in Ann. and Mag. Nat. Hist., ix. (1892) 
pp. 285-94 (8 figs ). 
1 Philosoph. Trans., 182b (1892) pp. 25-134 (17 pis.). 
