346 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Bpecies which nests in colonies in Germany. The eggs were artificially 

 incubated to secure a continuous scries. It was found that the inter- 

 medium and centrale arc not present in the grebe embryo. The tran- 

 sitory metacarpal iv. regularly occurs, and attains its greatest development 

 on the L5th day. The transitory metacarpal v. appears only on the 

 ll-12th day, and then atrophies. The grebes now living are descended 

 from ancestors which had hills of a pronounced Lotus type. 



Origin of White Blood-corpuscles and Spleen in Bufo vulgaris.* 

 II. Mietens has investigated embryos of the common toad, Bufo vulgaris, 

 with a view to determining the origin of the white blood-corpuscles and 

 the spleen. The white blood-corpuscles arise in three different ways : 

 (1) through differentiation from the primitive indifferent blood-cells. 

 which also give rise to erythrocytes, and perhaps to connective-tissue 

 elements ; (2) through a rounding off of mesenchyme-cells ; (8) through 

 the liberation of endocardial cells. In the larvae white and red blood- 

 corpuscles do not pass into one another. Myelocytes and lymphocytes 

 are modifications of the same lymphocyte-like original cells. The 

 developed liver does not play an important part in blood-making during 

 larval life. Leucocytes arise only from the mesenchyme around the 

 bile-duct. After metamorphosis, blood-production increases greatly. 

 The blood-cells, both red and white, arise from foci lying mainly between 

 the large veins and the bile-duct. There is no intra-vascular blood- 

 production. The sinus-like blood-spaces of the liver offer favourable 

 conditions for the increase and development of the leucocytes. The red 

 blood-corpuscles of the larva? correspond phylogenetically to the pigment- 

 elements which function in the earlier developmental stages in the higher 

 classes. The thymus arises through the migration of lymphocytes into 

 an originally epithelial rudiment, and a multiplication of these within it. 

 There is no production of white blood-corpuscles. The mesenterial 

 leucocyte-focus is an important seat of development of the leucocytes. 

 The white blood-corpuscles are differentiated from originally indifferent 

 mesenchyme elements. The leucocyte focus is localized round the 

 branchings of the intestinal vessels. It attains its greatest development 

 at the time of the metamorphosis. Multiplication of the white blood- 

 corpuscles takes place in the mesenchyme of the pronephros. The spleen 

 arises from a congregation of primitive migratory cells in the sheath of 

 the mesenteric artery near the place of its origin. The ccelom epithelium 

 plays a limited part in its origin. In the glomerulus of the pronephros 

 it was possible to detect elements which showed great similarity to 

 nerve-cells. 



Structure and Development of Posterior Lymph-hearts of Turtles.! 

 Frank A. Stromsten has studied the lymph-hearts of loggerhead turtles. 

 The development is initiated by the vacuolation of the post-iliac rnesen- 

 chyme-tissue in the second week. The spongy tissue thus formed is 

 invaded by capillaries from the caudal portion of the post-cardinal veins. 

 Near the close of the third week, parallel veno-lymphatic channels are 

 formed by the confluence of the mesenchymal spaces with each other 

 and with the invading capillaries. These channels anastomose freely and 



* Jena. Zeitschr. f. Naturw., lxiv. (1910) pp. 301-56 (2 pis.). 



t Publications Carnegie Inst. Washington, No. 132 (1910) pp. 77-87 (2 pis.). 



