2194 Journal of Applied Microscopy 



endothelial origin or whether the lymphoid cells of the structures migrate into 

 the bodies from without. Observations were made on adult Salamandra macii- 

 lata, the results obtained were far superior to those from the adult frog. In 

 the adult salamander the thymus has a large number of leucocytes, often actively 

 dividing, as well as the usual adenoid tissue. Also bars of connective tissue, 

 some intact blood vessels, and three kinds of structures usually called " Hassal's " 

 corpuscles. The types of these are as follows : (1) Small, not distinctive bodies 

 surrounding closed vessels showing both endothelial cells and a connective tissue 

 sheath strongly developed. ('2) Larger structures consisting of a single giant 

 cell, or masses of them, or of a closed cyst of giant cells showing concentric 

 structure. (3) Single large cells with abundant plasma crowded with larger and 

 smaller strongly staining and refractive granules. In the development of all 

 these structures the endothelial cells and usually the elements of the connective 

 tissue layer of the blood vessels and the leucocytes of the thymus play an active 

 part, while the blood corpuscles take an important but passive part, closely con- 

 nected with the various changes undergone by these bodies. The small blood 

 vessels and capillaries first change, the endothelial cells enlarge as to nuclei and 

 plasma and push into the lumen of the vessels until they greatly reduce or 

 entirely fill it. The vessels then break into fragments which are small and solid 

 or larger with blood corpuscles in their cavities ; later these corpuscles undergo 

 degeneration. The small concentric corpuscles arise from the solid fragments 

 of vessels. Those fragments containing blood corpuscles show three ways of for- 

 mation of these bodies. In the first the nuclei of the endothelium and of the 

 connective coat of the blood vessel become elongated and sickle-shaped, then 

 fall to pieces, showing a concentric arrangement. Leucocytes may penetrate 

 into these masses. The second product arises from those bodies containing 

 blood corpuscles ; separate corpuscles in the lumen of the vessels or in the little 

 bladder like cavity formed in the midst of the fragment of vessel enlarge, swell, 

 their nuclei increase greatly, even to filling the whole space of the cell, and finally 

 the nucleus begins to take the red stain of the cytoplasm, the latter becoming at 

 last a pale yellow. Finally the nucleus becomes pale and vacuolated and the 

 corpuscle may disappear entirely or become a wing-shaped structure leading 

 again to a concentric effect. These blood corpuscles are entirely absorbed by 

 broadening leucocytes, which engulf and digest them. The last part of the paper 

 concerns the ultimate fate of the concentric bodies, which is largely brought about 

 by. processes of phagocytosis, resulting in their complete involution. e. j. c. 



Halta, S. Relation of Metameric Segmenta- ^j^^ ^^^^^^ ^^^^ ^ ^1^3^ resemblance 

 tion in Petromyzon to that in Amphioxus 

 and in Higher Craniota. Annot. Zool. Japon. between the history of the mesoblast 



43~7. 19°-- in Petromyzon and in Amphioxus, in 



the earlier stages the differentiation of the mesoblast is exactly parallel, while 

 the later stages resemble the features of the higher Craniota. Thus the same 

 animal, Petromyzon, shows features that make it truly a connecting link 

 between the lower and higher types. a. m. c. 



n J ri AC -ii-o-H D r> a: T) .u ^ paraffin bath has been devised to be 

 Regaud, CI., and Fouilliand, R. Paraffin Bath , , , , • • n,, • , 



Heated by Electricity. Journ. Anat. and heated by electricity. 1 his, the mvent- 

 Physiol. 36 : 574-579, 3 figs., igoo. ors claim, possesses many advantages 



over gas and petroleum heat. It is 

 lighter and can be manipulated more easily. For saturating pieces, wire bas- 

 kets suspended by a wire in a paraffin bath are used. a. m, c. 



