296 SUMMARY OF CURRENT RESEARCHES RELATING TO 



phosis of their prolongations and of their protoplasm the different 

 elements. The differentiated prolongations assume the character of 

 glia fibrils ; from a single prolongation there probably arise several 

 fibrils, some of which remain in connection with the cell, whilst others 

 become free. The last stage of the glia metamorphosis consists of 

 cells without prolongations, and astrocytes (which probably remain 

 stellate), with differentiated prolongations and differentiated cell-body 

 {Astrocyten des Endtypus). The cell-body of many full-grown stellate 

 cells, but especially of this type of Astrocyte, is provided with comb- 

 shaped elevations, which on staining behave as glia fibrils. Round the 

 vessels the glia fibres form a more or less thickly interlacing net, similar 

 to glia adventitia, and, together with the continuations of the stellate 

 cells, they form around the nerve-cells and fibres a more or less close 

 network, the glia capsules, but penetrate neither into the interior of 

 the nerve-cells nor of the myelin. Especially rich in glia are the optic 

 nerve, chiasma, optic tract, and olfactory nerve, while the roots of the 

 spinal nerves are provided to a definite extent with glia fibres. An 

 account is also given of the structure and composition of the ependyme, 

 of the continuations of the cells of the ependyme epithelium, and of the 

 infundibulum. 



New Nerve Sheath in Sensory Nerves.* — A. Ruffini has found a 

 new nerve sheath, between Schwann's and Ilenle's, in the terminal tract 

 of the sensory nerve-fibres in man. He regards it as protective in 

 character, calls it the guaina sussidaria, and describes it in detail. 



Peripheral Cell-Groups in Spinal Cord of Reptiles.f — A. I. Sterzi 

 discusses the peripheral cell-groups which occur throughout the whole 

 length of the spinal cord in reptiles, metamerically arranged beside the 

 spinal roots, arising in development from the ventral column, and motor 

 in function. They may be compared to the spinal ganglia. 



Olfactory Cells of Lamprey4 — E. Ballowitz gives a detailed account 

 of the minute structure of the olfactory cells in Petromyzon fluviatilis, 

 describing the peripheral protoplasmic body, which bears long cilia, and 

 the central nerve-process, which pursues an irregularly curved course 

 between the loose basal portions of the supporting cells, and shows 

 varicosities. 



Endocellular Tubules.§ — Domingo Sanchez has previously directed 

 attention to what he regards as fine intra-cellular tubules in the intes- 

 tinal cells of certain Isopods. He returns to this subject and discusses 

 intra-cellular tubule {a) in the unicellular glands, (b) in intestinal 

 epithelium, and (c) in ganglion cells. These represent three distinct 

 groups of intra-cellular tubules which must be separately discussed. 

 The author's new instances are chiefly from the intestinal cells of slugs 

 and snails. 



* Zeitschr. wiss. Zool., Ixxix. (1905) pp. 150-70 (2 pis.). 



t Atti Soc. Toscana Sci. Nat., xx. (1904) pp. 243-75 (2 pis.). 



t Archiv Mikr. Anat., lxv. (1904) pp. 78-95 (1 pi.). 



§ Boll. Soc. Espaii. Hist. Nat., iv. (1904) pp. 375-9 (2 figs.). 



