288 S. Vincent. 



If a longituflinal section be taken through the centre of an 

 "axillary heart" of Scyllium canicula, it is seen that the whole 

 structure consists of two distinct parts. First, there is an elongated 

 nerve-ganglion antero-externally, and secondly, there is the proper 

 suprarenal medullary substance postero-internally. The ganglionic 

 structure needs little comment. It is composed of typical large 

 nerve-cells with nerve-fibres running longitudinally. The nerve-cells 

 are on an average 55 f^i in diameter. 



The typical arrangement of the proper glandular structure of the 

 axillary heart is as follows: — 



Running through the centre of the body is an arteriole. On each 

 side of the artery (surrounding it, forming a central zone) is seen the 

 layer of cells which are stained brown with the bichromate of 

 potassium. These are irregular and branched, and frequently more or 

 less triangular. Their size is difficult to state, owing to their 

 irregularity; they vary, however, in their greatest lengths from 

 10 — 30 f-i] the nucleus is usually about 6—8 /.i in diameter. These 

 cells appear to communicate freely together by their processes. 



The outer zone consists of an external layer of irregularly columnar 

 cells one row deep and beneath this one or two layers of polygonal 

 cells. Externally is a fibrous capsule 4 — 7 ,fi in thickness which sends 

 oif septa accompanied by capillary plexuses into the interior of the organ. 



There is no trace of an alveolar arrangement of the cells in 

 these bodies. 



In many cases there are groups of nei've-cells in the centi-al 

 portion of the structure, and scattered nerve-cells are not infrequent 

 in many parts of the organ. In addition, there are to be seen here 

 and there the intermediate form of cell to be described below. There 

 are many variations in the arrangements in regard to nervous structures, 

 and the amount of connection with the ganglia differs in different 

 genera and also to some extent in different species. The above 

 account, however, having reference to Scyllium canicula may be taken 

 as on the whole, fairly representative. 



The "axillary heart" is more "mixed up" with nervous structures 

 than any of the more posteriorly placed bodies. As we proceed 



