ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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several genera. As so much interest is attached to the presence of this 
set of teeth, he has thought it advisable to publish a preliminary account 
of his observations. After giving some details as to the various genera, 
he comes to the conclusion that traces of an earlier set are found in a 
large number of marsupials. These may be developed in connection 
with all the incisor teeth, the canines, and the first pre-molars, but these 
last are never calcified. 
The Human Tail.* — Prof. W. Waldeyer makes a valuable contri- 
bution to our knowledge of the much-discussed caudal appendage in 
man. Alike in the mature foetus and in the young child, tail-like out- 
growths from the coccyx are of not infrequent occurrence. In embryos 
from the first to the third month freely projecting tail-like outgrowths 
are well known. After a lucid discussion of what a tail really is, 
Waldeyer defines it as a portion of the body which contains caudal 
(i.e. post-sacral) vertebrae and sundry other derivatives of caudal seg- 
ments, and which is surrounded on all sides by integument. 
In 1880, Virchow distinguished, in reference to man, between tails 
with vertebrae and soft tails, and the distinction has been generally 
recognised. The early human embryo always shows a true or verte- 
brated tail, and this may persist even after birth. Yet no case is certain 
in which there are more vertebral bodies than in the normal coccyx. 
What occurs in tail-possessing human subjects corresponds to the distal 
non-vertebrated portion of the tail in other mammals, but there is no 
increase in the number of caudal vertebrae. This is true even in those 
cases where the caudal appendage is partly bony. 
Fixing of Ovum to Wall of Uterus. | — Herr Graf F. von Spee has 
studied this in the guinea-pig, where it occurs in the course of the 
seventh day after impregnation. The small size of the ovum (’08 mm. 
in diameter) renders its discovery by no means easy, and a series was 
obtained only after years. 
The inner lining of the uterus consists of cylindrical epithelium 
and two enslieathing zones of connective tissue — an outer looser and 
more fibrous layer surrounding the terminal parts of the glands, and an 
inner more compact layer traversed by the ducts of the glands. It is 
in this more compact zone that the ovum is implanted. Among its 
characteristics may be noted, further, the large number of dividing cells, 
the absence of matricial substance, and the abundance of fine intercellular 
clefts containing lymph. 
Shortly before fixation the ovum appears as a vesicle surrounded by 
the zona pellucida, with a germinal disc protruding into the interior, 
and with a delicate single-layered surrounding membrane which shows 
much thickened cells at the pole furthest from the germinal disc. These 
cells send plasmic processes through the zona pellucida, and thus come 
into direct contact with the uterine epithelium. In this region the 
epithelium disappears and the ovum becomes implanted in the connective 
tissue. Then, for the first time, there is a reaction on the part of the 
uterus ; for around the egg cell-division ceases, some cells become larger, 
the lymph-clefts become wider, and a lymph-space is formed. The 
* SB. K. Preuss. Akad. Wiss., 1896, pp. 775-81 (1 fig.). 
f Verb. Anat. Ges. X. Anat. Anzeig. Erg.-IIeft, xii. pp. 131-6. 
