^ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 2^ 



Formation of Filum terminale. — G. L. Streeter (Amer. Journ.. 

 Anat., 1919, 25, 1-11, 3 figs.). The filum terminale represents that 

 portion of the spinal cord caudal to the second coccygeal segment 

 (31st segment), which has undergone de-diflferentiation, and has finally 

 become converted into a fibrous strand. This strand, like the sacral 

 nerve roots, elongates by interstitial growth in adaptation to the ascend- 

 ing displacement of the spinal cord. The caudal tip of the dural sac- 

 maintains its relation to the vertebrai rather than to the spinal cord., 

 and remains attached to the filum terminale in the sacral region at a 

 more or less fixed point. J. A. T. 



b. Histology. 



Vital-staining of Tadpole's Tail. — Eleanor Linton Clark and 

 Eliot R. Clark {Anat. Record, 191«, 15, 231-56, 4 figs.). Neutra} 

 red, Bismarck brown and trypan blue are true vital stains affecting the- 

 tadpole's tail. The more highly diffusible dyes, neutral red and 

 Bismarck brown, stain the cells much more rapidly than does the- 

 coUoidal dye, trypan blue. But the latter can be preserved in per- 

 manent preparations. Neutral red and Bismarck brown stain granules 

 in the epidermis ; neutral red stains the contents of a richly branching" 

 sub-epidermal system ; trypan blue does not stain any of the cells of 

 the epidermis ; all three dyes stain an occasional granule in the walls of 

 certain blood-vessels ; all the three are deposited in the perinuclear 

 areas of the lymphatics, in certain large mononuclear wandering cells, 

 and leucocytes, and, to a less degree, on the processes of the stellate 

 connective tissue cells. Cells with the common property of phago- 

 cytosis react most readily to the vital-staining. J. A. T. 



Histogenesis of Blood-platelets in Yolk-sac of Pig'. — IT. E. Jordan 

 {Anat. Record, 1919, 15, 391-406). Blood-platelets are produced in the- 

 blood spaces of the yolk-sac and of the liver of the pig embryo by the- 

 primitive lymphocytes or hseraoblasts and their giant-cell derivatives^ 

 occasionally also by endothelial cells in process of differentiation into 

 haemoblasts and separation from the vessel wall. The mode of platelet- 

 formation is two-fold : (a) by segmentation of pseudopods, and {b) by 

 fragmentation of larger portions of cytoplasm. The giant-cells are 

 essentially hypertrophied hsemoblasts, and in the yolk-sac may function 

 as multiple erythroblasts. Blood-platelet formation appears to be a 

 by-product both of the normal activity and of the disintegration of 

 potentially erythrocytogenic giant-cells. Spindle cells of Ichthyopsid- 

 and Sauropsid blood, and platelets of Mammal blood apparently have a 

 similar function in relation to thrombus formation. They may be 

 considered as analogous elements, but no strict homology obtains. 



J. A. T. 



Origin of Phagocytic Mononuclear Cells. — F. A. McJunkin 

 {Amer. Journ. Anat., 1919, 25, 27-53, 3 pis.). These elements are 

 traced by means of injested carbon (lampblack) to the endothelium of 

 the blood-vessels. The demonstration of mitoses in endothelial carbon- 

 containing cells lining capillaries which are not lengthening is proof of 



