1890-91.] AMPHIBIA BLOOD STUDIES. 249 



the fusiform elements are found only in the blood of those animals which 

 contain nucleated red corpuscles.* 



III. The Origin of the H/Ematoblasts in Amphibian Embryo. 



There is probably no biological subject on which there is a greater 

 diversity of view than that of the origin of the blood corpuscles in the 

 embryo and adult vertebrate. The views on this point have multiplied 

 greatly within the last five years and as they have not much in common, 

 a resum^ of them can hardly serve any useful purpose in a paper so 

 limited in its scope as this one is. The observations, nevertheless, which 

 have been already published as to the origin of the haematoblasts in Fishes 

 and Amphibia have an important bearing on the facts which I am about 

 to describe and I shall, therefore, give here an outline sketch of them be- 

 fore proceeding with the description cf my own observations. 



Goettej- found the blood cells arise in the mass of the yolk cells. On 

 the under and lateral edges of the yolk mass in Batrachian larvae blood 

 cells are formed by the breaking up of the large peripheral yolk cells into 

 smaller ones, and at the same time there separates from the inner side of 

 the visceral layer a number of cells forming a covering for the groove in 

 the yolk in which the blood cells are developed. As the interstitial 

 fluidity of the mass increases it extends over the yolk and affects 

 the surrounding tissue just in the same manner as the interstitial 

 fluid shapes the origin of the primary vessels, producing pouch-like 

 diverticula connected with one another, from the yolk vessels. Goette 

 regards the red and white cells of the spleen as direct descendants of the 

 yolk cells. 



Davidoff;]: reservedly expresses the view that the yolk spherules give 

 origin by, possibly, protoplasmic transformation to parablastic elements 

 and that the latter develop, in many cases, into blood cells. On this view 

 the nucleus of the blood cell is but a yolk spherule imbedded in a proto- 

 plasmic basis, and Davidoff thinks that this is, in a sense, a confirmation 

 of Brass' theory that the chromatin of the nucleus of every cell is secreted 

 or stored up food material. 



* As the red corpuscle in mammalia is comparatively a fragile element its disintegration can 

 scarcely involve the survival of any formed or structural element. If the fusiform element is the 

 nucleus and a small portion of cytoplasma of the red cell in lower vertebrates, we may suppose 

 since the platelets of mammalian blood are recognised generally as the homologues of the fusi- 

 form cells that the former are nuclei which have been extruded from haematoblasts, an extrusion 

 which Rindfleisch and Howell observed. 



t Entwicklungsgeschichte der Unke. 



t Ueber die Entstehung der rothen Blut Korperchen und den Parablast von Salamandra 

 maculosa. Zoologischer Anzeiger, 1884, s. 453. 



