256 , DE A. J. WHITING ON THE 



relatively thick, and formed of interlacing bundles of white fibrous tissue containing 

 many lymphoid cells and many large blood-vessels and nerves. The innermost layer is 

 denser and thinner than the others (it is about one-fifth the thickness of the inter- 

 mediate layer), and is composed of unstriped muscle fibre cells that are rendered con- 

 spicuous by staining deep-pink with cosine. 



Joining the under surface of the lower muscular layer are delicate, open, fibrous strands 

 that consist mainly of spindle cells, many of which are muscular. These strands are con- 

 tinuous with others that form a nearly regular meshwork, and which divide the paren- 

 chyma into a series of polygonal areas. In the middle of each area is an arteriole or a 

 capillary blood-vessel enveloped in its special sheath. 



The hilar sheath is very strongly developed in the teleostean spleen ; its peripheral 

 portion is distinctly muscular. The fibrous strands that bound the polygonal areas are 

 apparently derived from this outer portion of the hilar sheath. 



In the Frog the tunica propria consists of white fibrous tissue arranged more or less 

 distinctly in bundles. Scattered throughout its substance are spindle-shaped fibre cells, 

 which are almost certainly muscular. These are specially noticeable immediately 

 under the tunica serosa and also adjoining the parenchyma, as in the capsule of the 

 cod's spleen. Imbedded within the substance of the tunica propria are numerous very 

 large venous sinuses which are connected by somewhat large branches with the 

 venous sinuses of the pulp. Around the capsular blood-sinuses the spindle-shaped 

 fibre cells form a comparatively thick layer which stains pink with eosine, and is 

 undoubtedly muscular. There are no true trabeculse. The only representative of the 

 supporting framework in the interior of the spleen is a relatively small amount of 

 fibrous tissue forming a sheath for the blood-vessels. 



In the Tortoise the tunica propria consists of two layers, the outer composed of 

 white fibrous tissue staining faintly blue with hsematoxylin, and the inner composed of 

 unstriped muscle staining deeply with eosine and picric acid. The outer looser layer 

 contains a few large, clear, faintly stained lymphoid cells ; in the inner layer immedi- 

 ately subjacent to the outer layer there are venous sinuses somewhat larger than those 

 in the frog, and like them surrounded by muscle. There are no true trabeculse. The 

 arteries run in a thick fibrous sheath, which externally is strongly muscular, corre- 

 sponding with the inner layer of the capsule. Immediately surrounding the artery 

 is a layer of loose areolar tissue containing a few clear lymphoid cells corresponding, 

 therefore, with the superficial layer of the capsule. 



In the Grass Snake the tunica propria is composed of dense fibro-muscular tissue. 

 It consists chiefly of white fibrous tissue towards the surface, while deeper it is almost 

 entirely muscular. Within the muscular portion large venous sinuses are very numerous, 

 as in the skate, frog and tortoise. Where the muscular portion joins the parenchyma, 

 its fibres separate so as to form elongated meshes in which are rows of lymphoid cells. 

 Four broad trabeculas-like processes, somewhat wedge-shaped, composed of tissue 

 resembling that of the deeper portion of the tunica propria, but more loosely arranged, 



