386 SUMMARY OF CURRENT RESEARCH KS RICLATING TO 



abortive second division, but the chromosomes about to be rejected are 

 seen to return again to the ovum and re-unite with their former 

 neighbours. In the case of the bee's parthenogenetic ova (those that 

 develop into drones) there is a second maturation division, and the 

 number is reduced to half the normal. In the spei'matogenesis of the 

 drone the second matm'ation division is suppressed, and there is no 

 reduction. The author's conviction is that the first maturation division 

 is homeotypic, separating bivalent chromosomes, while the second is 

 heterotypic and reducing. J. A. T. 



Dictyokinesis in Germ-cells. — R. J. Ludford and J. Brontk 

 GateJsBY {Proc. Roy. Soc, London, 1921, 92, 235-44, 2 pis.). Most 

 animal ctlls show two categories of cytoplasmic inclusions — the mito- 

 chondria and the Golgi apparatus. The latter generally takes the form 

 of an excentric juxta-nuclear system or network, composed of rodlets, 

 platelets or beads, arranged, in many cases, around and over the surface 

 of the centrosphere or archoplasm, in which lies embedded the centro- 

 some. In highly differentiated cells such as the oocyte or the nerve-cell, 

 the Golgi apparatus becomes dispersed into the fartliermost parts of the 

 cell-cytoplasm, and in most cases therefore loses its relationship to the 

 centrosome. The Golgi rods or dictyosomes are divided in mitosis, 

 but they are very elusive during the process. The authors have 

 followed the distribution or dictyokinesis in various types. It is some- 

 times very irregular, notably in mammals. In contrast with karyo- 

 kinesis it does not entail any sort of fission of individual elements as 

 occurs with chromosomes, but merely an unprecise sorting out of parts 

 of the Golgi reticulum between the two daughter-cells. Everything 

 indicates that the Golgi apparatus takes a part less precise and less 

 important, in the hereditary processes of the cell, than that fulfilled by 

 the chromosomes. J. A. T. 



Transplanting Sections of Spinal Cord. — S. K. Detwiler (Froc. 

 Nat. Acad. Sci., 1920, 6, 695-700, 2 figs.). In Ambli/stoma embryos 

 the portion of the spinal cord from w^hich the normal brachial plexus is 

 derived (third, fourth and fifth .segmental nerves) was removed, and 

 there was transplanted into the excised area a more posterior portion of 

 the spinal cord of another embryo — the portion that normally gives 

 origin to the seventh, eighth, and ninth segments. These nerves, in 

 their normal position, are capable of producing but very limited move- 

 ments when innervating transplanted limbs. Now in the embryos 

 operated on the limbs performed normal adaptive and co-ordinated 

 movements in 50 p.c. of cases. A microscopic study showed the 

 presence of a perfectly developed brachial plexus with normal intrinsic 

 nerve distributions. Moreover, the nerves were larger than the normal 

 seventh, eighth and ninth. Even the cord itself and the spinal ganglia 

 showed distinct hyperplasia of the nerve-cells, thus indicating that the 

 hypertrophic development was due to excessive piroliferauon of the 

 neuroblasts rather than to a compensating increase in the volume of a 

 specific number of cell bodies and their axons. The factor involved in 

 the over-production of the motor-cells is the stimulus afforded by the 

 connexion with the central neurones (bulbo-spinal fibres). J. A. T. 



