148 SUMMARY OF CUREENT REEARCHES RELATING TO 



Blastodermic Vesicle of Mammals.* — CI. Schlater sums up his 

 conclusions in the following propositions. 



1. The ova of Sauropsida, Placentals, Monotremes, Marsupials, and 

 Amphibians have evolved quite independently from large Piscine eggs, 

 rich in yolk, with partial unequal segmentation. 



2. AH these main types of ova were simultaneously represented 

 among the primitive terrestrial Vertebrates, the Protamuiota. 



3. All the Protamniote types of ovum show at the end of the seg- 

 mentation a differentiation of an external cell-layer, which takes no 

 further share in forming the embryo, but effects connection with the 

 mother (Hubrecht's trophoblast). 



•4. In Amphibians and Sauropsida the trophoblast comes to nothing, 

 and is even rudimentary. In Mammals only does it attain full develop- 

 ment. It is the main factor in forming the placenta. 



5. The blastodermic vesicle of Placentals is formed at the end of the 

 Morula stage, the trophoblast exhibiting superficial expansion, the em- 

 bryonic streak or primordium lagging behind as to growth, and fluid 

 accumulating between the two. The formation of the blastodermic 

 vesicle is a very ancient and primitive process. 



6. In its earliest phases the blastodermic vesicle may have had two 

 independent modes of development. A very rapid active penetration of 

 the trophoblast into the maternal mucous membrane, and a very early 

 vascularisation, may have resulted in a quite small blastodermic vesicle, 

 while a loose superficial connection, and a late vascularisation, may have 

 led to a large blastodermic vesicle. Between these two types there are 

 transitional types. The Primates illustrate the first type. 



Structure of Early Human Embrycf — E. Bonnot and R. Seevers 

 describe an embryo of 11 mm., supposed to be about thirty-three days 

 old. Some facts of special interest may be quoted. The heart is 

 relatively six times as large (in volume) as in the new born, and more 

 than seven times as large as in the adult. The volume of the spinal cord 

 is about forty-four times as large, relatively, as in the newborn, and 115 

 times as large as in the adult. Certain important features in the blood- 

 vessels are noted. The dorsal aorta is formed by the union of the two 

 lateral aortic arches, just below the origin of the subclavian (vertebral) 

 arteries. At its origin it is comparatively narrow, but gradually enlarges 

 until its diameter is at least twice as great towards its lower end. A 

 branch from the vitelline vein extends into the mesentery, and evidently 

 represents the superior mesenteric vein of the adult. The vitelline 

 vein, distal to the duodenum, shows signs of involution ; that it does 

 not persist as the superior mesenteric vein, has evidently been overlooked 

 by many later wi'iters. 



Development of Ornithorhynchus.| — J. T. Wilson and J. P. Hill 



give an abstract of the results of their investigations upon the intra- 

 uterine development of the egg of Ortiithorhynchus. One or two points 

 of special interest- may be specified. There is a very early differentia- 



* Anat. Anzeig., xxx. (1907) pp. 8-19 (1 fig.). 



t Op. cit„ xxix. (1906) pp. 452-9 (3 figs.). 



X Proc. Roy. Soc, Series B, Ixxviii. (1906) pp. 313-15. 



f 



