692 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
pared for two cell-divisions, the second immediately succeeding the first. 
Before division the amount of nuclear material is the same in the two 
sets of cells. During the two divisions there is no multiplication of 
nuclear substance; the results of division have only half as much 
nuclear material as there is in ordinary nuclei after dividing once. The 
number of chromatin elements in the nucleus of the mother-sperm-cell 
and in the germinal vesicle is the same as that of an ordinary nucleus 
at the middle of division, or double that of a nucleus in the preparatory 
stage of division. But the morphological value of these (germinal) 
elements is different, in consequence of an origin divergent from the 
normal process. For while eight daughter-chromosomata normally 
arise from the simple longitudinal cleavage of four filaments, here they 
arise by the double longitudinal cleavage of only two. Yet these two 
contain the same amount of material as the four formed by transverse 
division at the beginning of karyokinesis. Since the immature ovum 
and the mother-sperm-cell go through the same processes of nuclear 
division, with all their divergent characteristics, in precisely similar 
fashion, the products of division must also have the same morpho- 
logical rank. The two daughter-sperm-cells correspond to the ovum 
and the first polar body ; the four spermatozoa are comparable to the 
ripe ovum, the second polar body, and the two spheres arising from the 
division of the first ; the polar bodies have therefore the morphological 
rank of rudimentary egg-cells. 
Prof. Hertwig then asks whether the processes observed in the 
spermatogenesis of Ascaris occur elsewhere, and whether the formation 
of polar bodies is genuinely a double division of cell and nucleus. 
In the second part of the memoir he criticizes the theories of Minot, 
van Beneden, Weismann, Boveri and others, and enters into a long dis- 
cussion of the facts and theories in regard to polar bodies. His own 
opinion is that they are abortive ova, that their production is com- 
parable to that of spermatozoa from a mother-sperm-cell, and that their 
persistence is explained by the physiological importance of the reduction 
which they effect in the mass of the germinal vesicle. 
Development of the Primitive Kidney in Man.* — Dr. H. Meyer 
has been able to study the development of the mesonephros in a human 
embryo of the first month. He describes the mesonephric ridge, which 
did not exhibit either on its external or internal margin any thickening 
or double layer of epithelial cells. The proximal part of the Wolffian 
duct arises from the mesoderm and is at first united to the pleuro- 
peritoneal epithelium, while its distal portion is united to the ectoderm. 
It is here, as elsewhere, a tubular communication between the body- 
cavity and the surface, and its ends are separated by the longitudinal 
growth of the embryo. The mesonephric canals and the Malpighian 
bodies are then described. Each segment of the mesonephric blasteme 
has three connections With the elements of the median plate or future 
peritoneal epithelium, with the cells of the corresponding primitive 
segment, and with the wall of the aorta. The first two connections 
show that the blasteme consists of elements both of the median and of 
the segmental or protovertebral plates. 
* Arch. f. Mikr. Anai, xxxvi. (1890) pp. 138-72 (2 pis.). 
