434 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
These lobules appear to represent the Malpighian corpuscles. In the 
angles between them the connective tissue fibres separate so as to- 
leave small spaces in which a few blood-cells are to be seen. (Fig. 6, 7). 
The brown pigment patches have increased in size so as in many in- 
stances to entirely conceal the tissue surrounding the artery, and 
render its nature difficult of determination. In places where there is no: 
pigment, (Fig. 6) the endotheloid cells are visible, covered by only a few 
lymphoid cells, and so they rather resemble the pulp. The thickness 
ot the stroma between the lobules varies from 6°4 to 55-8, and the 
average diameter of the enclosed spaces is 220 p. 
This connective tissue forms a thick layer beneath the outer 
capsule, from which it is easily distinguished by its lesser density. 
As its fibres pass inwards between each outer Malpighian corpuscle, 
they draw the capsule slightly after them and give in section a wavy 
outline and the appearance of minute papille on the surface, referred. 
to above. The difference in transparency is readily accounted for by 
the difference between connective tissue and large numbers of vesicu- 
lar spaces filled with blood. 
I regret that the short time at my disposal for the preparation of 
this paper has prevented my preparing sections from a large number 
of specimens so as to examine the steps in the change. Fig. 4, s¢., 
shows a trace of the beginning in the pulp. The difference was also. 
noticeable in making preparations of the vessels, for while in the one 
case the substance of the gland was readily removed by a camel’s 
hair brush, in the other it was tough and difficult to clear away. 
The most marked difference between the spleen of Amturus and 
the same organ in higher Vertebrata is the absence of any structure 
corresponding to the trabecule. 
THE THYROID GLAND. 
In Amiurus this organ occupies the exact position described for it 
by Stannius' in the Ganoids and many Teleosts, viz., beneath the 
copule of the branchial arches and surrounding the anterior end of 
the branchial artery. It is an impair structure extending in the 
median line from the origin of the vessels to the first pair of gill 
arches to a short distance behind the origin of the single stem for 
the third and fourth pairs of arches. Although richly supplied with 
blood it appears of a whitish colour contrasted with the blood vessels. 
1 Loc. cit., page 255. 
