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SUMMARY OF CURRENT RESEARCHES RELATING TO 
body in the yolk known as vitelline nucleus, but quite distinct from the 
proper nucleus of the egg. In the fresh state it is almost impossible to 
perceive any trace of this body, but after treatment with dilute acetic 
acid the structure can be easily seen. Examined with a high power it is 
found to consist of a spherical collection of minute granules. It does 
not appear to be present in the youngest ova, but becomes visible when 
they have reached a certain definite size. It makes its appearance in the 
form of a few granules close to the wall of the germinal vesicle, and as 
the egg becomes larger it is gradually more and more separated from the 
latter, while increasing in size and opacity. A history is given of the 
ovum in a flat-fish from the time of its first origin in the germinal 
epithelium to the stage in which, it is almost ready for extrusion. This 
history is probably almost exactly similar in all fishes which produce 
pelagic eggs and have an annual spawning season. The ova of the 
pipe-fish have been examined, and they have been found to have as many 
as four vitelline nuclei. 
Pronephros of Salmonidse.* — Dr. J. Sobotta finds that the pronephros 
of the trout arises from a diverticulum of the body-cavity in the region 
of the fifth and sixth segments. It lies at first laterally and dorsally, 
but subsequently takes up a wholly dorsal position above the gut. It 
appears after the enclosure of the yolk is completed, later than the 
pronephric duct, and is slowly but wholly shut off from the body-cavity. 
At the time of the first heart-beat it . is divided into (1) a median part 
— the future chamber; and (2) a lateral part, in direct continuity with 
the pronephric duct — the secreting canal portion. The latter comes to 
be connected with the chamber by a simple funnel-like opening. From 
cells lying between the chambers of the two sides, a blood-vessel 
is formed ; this invaginates the walls of both, and forms the glomerulus. 
Meantime the anterior part of the duct, which is at first straight, is bent 
upon itself in a loop, and this looped part enters into an important 
connection with the anterior ends of the cardinal veins, projecting into 
them. A series of single vasa afferentia arise from the aorta, but there 
is no special renal artery. This primitive state of affairs represents for 
a considerable time the whole excretory system. 
B. Histolog-y. 
Cytotropism.| — Prof. W. Eoux reports the results of his recent ex- 
periments on frogs’ eggs. These eggs were teazed apart and observed 
under precautions necessary to prevent currents and jars in the liquids. It 
was found that movements may take place which result in the union of 
some of these isolated cells. These movements are gliding or creeping 
in form. In many cases, especially when salt solution is used, the cells 
throw out pseudopodia, which may anastomose with pseudopodia of other 
cells. “ In detail these movements are found to be of limited extent, but 
yet capable of resolution into considerable complexity.” Only cells 
having diameters of from 20 to 60 [a show the phenomena, and then 
only when not more than their own diameter apart. Many cells may 
* Anat. Anzeig., x. (1894) pp. 333-6 (2 figs.). 
t Arch. f. Entwickhingsmechanik, i. (1894). See Amer. Natural., xxix. (1895) 
pp. 385-7. 
