944 SUMMARY OF CURRENT RESEARCHES RELATING TO 



occurred. Dcfinito injuries to tho ovum produced definite defects in 

 the embryo. Many portions of the embryo seem to exhibit self- 

 differentiation. Tho nature of tho injuries makes a report of their 

 details difficult : the above illustrates their general character. 



/3. Histologry.* 



Nuclear Division in the Spinal Cord.f — Prof. A. Eauber seeks 

 to answer tho following questions : — Are the figures of nuclear mitosis 

 observed in the spinal cord, similar to those observed elsewhere ? do 

 other than mitotic modes of division occur ? in what layers of the 

 medullary cord do the nuclear divisions occur ? what axis or axes of 

 division predominate ? at what stages, &c, do the mitoses occur ? His 

 research, so far as communicated, relates to the Batrachia. 



Historical. In 1881, Altmann's researches on the embryology of 

 the chick seemod to lead him to these striking conclusions : — (a) that 

 all diverticula of ectoderm and endoderm, and these two layers them- 

 selves when more than one stratum thick, exhibited nuclear division 

 only in that layer which represents the outer side of the original 

 ectoderm or endoderm — in the stratum, in other words, furthest from 

 the mesoderm. The spinal cord thus exhibits nuclear division only 

 in the layer next the central canal, (b) The planes of division are 

 almost exclusively parallel to the bounding surface. The cells 

 multiply in a superficial direction, and not in the direction of the 

 thickness. The first result suggested at once, among other questions, 

 an inquiry as to the nutritive supply which determined the occurrence 

 of proliferation in such a position, nor is the second result less striking 

 in its suggestion that the increase in thickness is really secondary, 

 and dependent on the displacement of the cells which multiply only 

 in a superficial direction. After discussing the import of these 

 results, Eauber traces the course of research, showing how Uskoff 

 fully confirmed Altmann, while Pfitzner describes nuclear figures 

 through the entire thickness of the wall. In 1882 Eauber noted the 

 presence of mitosis in all the layers, and even most abundantly in the 

 outermost. Vignal, however, again confirmed the results of Alt- 

 mann and Uskoff, to which the research of Kogane'i on the retina 

 was also, for the most part, corroboratory. A recent research on the 

 embryo of Tropidonotus natrix by Merk, also partially supports the 

 conclusions of Altmann. In the spinal cord of this form there is a 

 single proliferating layer, furthest from the mesoderm, next the 

 central canal. In the brain and in the retina this ventricular proli- 

 ferating layer is present only in the earlier periods of development ; 

 afterwards the deeper layers also exhibit figures of division, which are 

 then more or less absent from the ventricular sheath ; at different 

 periods the position of proliferation changes. In the cerebellum, 

 division occurs, from the first, in all the layers. Merk has thus 

 demonstrated the existence, in brain and retina, of " ultra- ventricular " 

 mitoses. 



* This section is limited to papers relating to Cells and Fibres, 

 t Arch. f. Mikr. Anat., xxvi. (1886) pp. 622-44 (1 pi.). 



