1074 UR. H. WATNEY ON THE MINUTE ANATOMY OF THE THYMUS. 
The cells become gradually smaller and less distinct, until at length they look like 
round nuclei, and have lost their epithelial character; at the same time there is an 
ingrowth of vessels and connective-tissue in the thick wall of the organ. As regards 
the further development of the gland, Kolliker agreed with the views of Simon (2). 
Besides the thymus, he found in embryoes of fifteen, sixteen, and seventeen days, an 
accessory thymus as a double organ between the oesophagus and the trachsea ■ this 
organ showed hollow spaces and vessels in the embryo of seventeen days old. In an 
embryo of fourteen days he found another organ like a thymus before the first arch of 
the aorta. In an embryo of sixteen days, he found the lateral part of the thyroid 
consisted of two parts—one was in its usual place, the other on the side of the carotid, 
and behind the upper end of the thymus. 
His (52), 1880, gave drawings of closed rings of epithelium, which he said probably 
form the thymus. In a footnote he said that the acinous form of the gland is thus 
explained; that the adenoid tissue arises from the surrounding connective-tissue, and 
that the concentric corpuscles are the remains of the epithelium. 
Stieda (53), 1881, examined the thymus of many young Mammalian embryoes ; he 
demonstrated and figured the thymus as arising from one of the branchial clefts (pro¬ 
bably the third) as a hollow epithelial tube; around this tube there is a connective- 
tissue envelope, and between these two adenoid tissue is developed. He found it 
impossible to trace the epithelial elements; but he thought that the concentric 
corpuscles and the large cells are the remains of the original epithelial layer. 
Opinions of various authors concerning the so-called plasma cells. 
Waldeyer (77), in 1875, described cells with coarse granules, which are often 
found near the blood vessels; they are easily transformed into fat cells; he called them 
plasma cells. 
Flemming (78), in 1876, found that plasma cells are more numerous in some animals 
than in others; he did not deny that they form fat cells, but he thought that they 
much resemble atrophied fat cells. 
Ehrlich (79), 1877, used an aniline dye, dahlia , to trace out the plasma cells; he 
found that they do not contain fat; he noticed them, among other places, in the 
thymus of the Calf, where they have the form of lymphoid cells. 
Lowe (80), 1878, considered that the granules in the plasma cells are not fat 
granules, but the precursors of fat. 
Ehrlich (81), 1879, showed that the cells, all classed by Waldeyer as plasma cells, 
are probably not all of a similar nature; he considered that certain of these cells 
should be classed separately; they are characterised by their containing granules 
which are very readily stained by aniline dyes. 
There have been two other papers on these subjects by Westphal (82) and 
Schwarze (83), neither of which I have been able to obtain. The last author said 
