1890-91.] AMPHIBIA BLOOD STUDIES. 251 



Riickert* gives a full description of the origin of the blood cells in 

 Torpedo embryos. He found them to arise in the peripheral mesoblast 

 where they constitute groups situated in cavities formed between the 

 spindle-shaped mesoblastic cells. Where the outer and inner layers of 

 the blastoderm are closely applied to the yolk these groups give off cells 

 which constitute the blood islands of the posterior germinal area. At the 

 latter point, according to Riickert, there can be no doubt about the origin 

 of the blood cells out of the mesoblast. Laterally, and in front where 

 the mesoblast is thin, the formation of the blood and of the vessels occurs 

 through the accession to this part of freshly divided yolk cells (merocytes). 

 Far anteriorly, the merocytes may be very large in size and appear then 

 as megaspheres. The latter may, through unequal, indirect division, bud- 

 ding and fragmentation, give also origin to blood cells and mesoblast. 



This brief sketch of the various theories as to the method of blood 

 formation and the origin of blood cells shows how discordant they are. 

 Goette believes that the peripheral yolk cells break up into haematoblasts 

 Davidoff thinks that yolk spherules become the nuclei of the red cells 

 and that the discoplasma is derived from transformed protoplasm of 

 the yolk, Wenckebach and Ziegler considered that the haematoblasts are 

 of mesoblastic origin wholly, while Riickert is apparently disposed to 

 believe that they are derived from the yolk cells on the one hand and 

 from the mesoblast on the other. 



As far as my observations on the Ambly stoma larvae go they are in 

 accord with those of Wenckebach and Ziegler on Teleostean embryos, as 

 to the derivation of the haematoblasts from the mesoblast alone. 



The first blood corpuscles of the Amblystoma larvae appear at about 

 the twelfth or thirteenth dayf after the deposition of the ova. At this 

 date the heart is in the process of formation, the endothelial portions 

 of it being derived from the entoblast in the manner described by 

 Rabl:|: for Salamandra and Triton. The heart cavity, for thirty-six hours 

 after this, even when fully formed, contains no cellular elements of any 

 sort. The first blood vessels to be formed appear also at the twelfth day, 

 constituting the subintestinal veins§ and it is in association with the 

 formation of these that the haematoblasts make their appearance. 



* Ueber die Anlage des mittleren Kiemblattes und die erste Blutbildung bei Torpedo. 

 Anat, Anz. , 1887, Nos. 4 and 6. Also : Weitere Beitrage zur Keimblattbildung bei Sclachiern. 

 Anat. Anz., 1889, No. 12. 



+ These dates are only approximate as there is a great variation in the development of the 

 larvae in the same mass of eggs. 



JMorph. Jahrbuch, Bd. XII. p. 252. 



§The occurrence of tvs'o subintestinal veins ,instead of one in Selachii was first pointed out 

 by Mayer (Mitth. ans des Zool. Stat, zu Neapel, Vol. VII., p. 340) and subsequently by Riickert 

 {loc . cit.) 



