ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
579 
latter is inter-, the former is intra-trabeoular. This latter attains an 
extraordinary development and the contents of the vessels of the two 
sets is quite different. The intra-trabecular plexus serves as a sub- 
stratum for the multiplication of red cells, and the author proposes, 
therefore, to call it the haematopoetic capillary plexus. 
Within the vessels are found, firstly, erythroblasts ; these give rise 
to the red cells and have the form of elements with a characteristic, 
rounded nucleus, abundance of chromatin, arranged in a plexus ; there 
is not much protoplasm, and what there is is homogeneous. The first 
erythroblasts of the liver are derived from young nucleated red cells 
which exist from the time of the appearance of blood in the embryo ; 
they are more or less charged with haemoglobin, but, later on, the 
products of their multiplication are colourless erythroblasts. The 
formation of new erythroblasts is effected by indirect division of pre- 
existing elements of the same kind ; as long as the liver has its primitive 
character this multiplication is not very active. It becomes more 
marked on the appearance of the haematopoetic plexus. The conversion 
of erythroblasts into adult red corpuscles is effected by a series of 
changes of the nucleus and protoplasm which end with the removal of 
the nucleus. 
After leaving the blood-corpuscle the free nucleus undergoes a series 
of changes ; 'these are modifications of retrogression or normal degenera- 
tion ; they end with the complete destruction of the nucleus which is 
effected either by chromatolysis or by phagocytosis. On the whole it 
would appear that the embryonic liver is just as much a haematopoetic 
organ as the osseous medulla of Birds. 
The next of the contents of the vessels are the white cells ; the leuco- 
blasts are said to be characterized by the structure of their nucleus, 
the appearance of their protoplasm, and by the great delicacy of their 
cell-membrane ; in the early stages of hepatic development the white 
cell is a phagocyte, and tabes part in destroying the freed nuclei of the 
erythroblasts. The liver has probably some influence on the multipli- 
cation of leucoblasts ; especially in very young embryos. 
The last constituent is represented by the giant-cells ; their proto- 
plasm is often differentiated into distinct layers ; vacuoles are present ; 
the cellular contours are sometimes very irregular ; the cells may 
exhibit prolongations in the form of pseudopodia or of finer processes ; 
the cell is not bounded by a true membrane. These giant-cells take 
part in the destruction of the nuclei of the red corpuscles, being absorbed 
by phagocytosis. Some of the cells bud but they take no part in forming 
the red corpuscles. The giants multiply by direct division into two or 
into several daughter-cells similar to the parent cell ; they are not 
retrograding elements, but cells with an independent existence, with a 
definite part to play, and multiplying like other cells ; they appear to be 
derived from the leucoblasts. 
B. Histology. 
Structure of the Cell.* — Dr. C. C. Schneider has studied the ova of 
Sfrongylocentrotus, Ascaris , Tiara , &c., the young male-cells of Astacus 
and Ascaris , besides Trichoplax adhserens , Vorticella , &c. The cells 
* Arbeit. Zool. Inst. Univ. Wien (Claus), ix. (1891) pp. 179-224 (2 pis.). 
