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, i). 

 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 

 of the stroma between the lobules varies from 6'4 to 55'8/j., 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 papillse 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, st., 

 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'& 

 hair brush, in the other it was tough and difficult to clear away. 



The most marked difference between the spleen of Amiurus and 

 the same organ in higher Vertebrata is the .absence of any structure: 

 corresponding to the trabecuke. 



THE THYROID GLAND. 



In Amiurus this organ occupies the exact position described for it 

 by Stannius 1 in the Ganoids and many Teleosts, viz., beneath the- 

 copulae 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 hoc. cit., page 255. 



