602 SU-MMA.RY OF CURRENT RESEARCHES RELATING TO 



&. Histology. 



Reissner's Fibre.* — George E. Nicliolls gives a detailed account of 

 his observations on Reissner's fibre and the sub-commissural organ in 

 the Petromyzontidffi and Myxinoids. Speaking of it generally as it occurs 

 in Vertebrates, he writes as follows : — " It arises from the speciaUzed 

 epithelium of the sub-commissural organ, which has markedly the 

 character of a sensory epithelium. It is first discernible at a point far 

 forward beneath (anterior to) the posterior commissure, where it is 

 formed by the coalescence of numerous fine fibrillas, resembling long 

 cilia, from the elongated ependymal cells; these fibrilla3 continue to 

 join it along its whole course beneath the posterior commissure (and 

 possibly also in the canalis centralis) ; but it never arises, either wholly 

 or in part, from any point in the brain dorsal (posterior) to the posterior 

 commissure in any form studied, except, perhaps, in a comparatively 

 few cases (e.g. Selachians and Myxinoids), where the specialized 

 ependymal epithelium also may extend on to the dorsal (posterior) 

 surface of the posterior commissure." The fibre extends freely through 

 the fourth ventricle, from which it passes into the canalis centralis to 

 end in the sinus terminalis. In the lamprey, where the fibre has been 

 traced with absolute certainty to its end in the sinus terminalis, it is 

 attached at frequent intervals in the canalis centralis to the ependymal 

 epithelium by cilia, which appear to have fused with the fibre, and are 

 probably actually constituent parts of it. Attention may be directed to 

 some of the exceedingly interesting photomicrographs, e.g. that of 

 Geotria austraUs, from one of Prof. Dendy's preparations, showing a 

 great length of Pieissner's fibre lying in the fourth ventricle and canalis 

 centralis. 



Study of Leucocytes. t — L. Merk has studied human leucocytes from 

 fresh pus or in the blood, observing them in a dark field. Two peculiarities 

 stand out. The neutrophil granules, and perhaps also the basophil 

 granules, fill the leucocyte in the form of exceedingly clear refractive 

 spherules, which appear in very active movement, like the air-bubbles 

 in the foam of a water-fall. Merk gives them the name granula aestuantia. 

 The second peculiarity, which occurs independently of the first, is the 

 appearance of the living leucocyte of extraordiuarily long and extremely 

 fine processes, which Merk calls trichopods. They sometimes stream out 

 like a brush from part of the cell. 



Shrinkage of Vesicular Cells in Ossification of Cartilage, t — 

 Brodersen has studied the changes in the vesicular cells at the cartilage- 

 bone boundary at the end of the femur of a young hare. Each vesicular 

 cell was surrounded by a zone of rods. These spread like a mantle 

 around the whole of the shrinking cell. They form a thick envelope 

 around the nucleus and cytoplasm, which are no longer distinguishable 

 from one another. The rods then disappear, as the cell becomes com- 

 pletely collapsed. Brodersen regards the shrinking as altogether due 



* Quart. Journ. Micr. Set., Iviii. (1912) pp. 1-116 (5 pis.). 

 t Arch. Mikr. Anat., Ixxx. (1912) pp. 561-86 (1 pL). 

 X Anat. Anzeig., xli. (1912) pp. 409-15 (2 figs.). 



