672 ANATOMY OF THE MUZZLE OF ORNITHORHYXCHUS, 



In his recent paper Poulton has entered more fully into their 

 histological structure, but from the unsatisfactory nature of the 

 material at his disposal, there remain some points which he was 

 unable to elucidate, and others which we are convinced he has 

 erroneously interpreted 



As stated by Poulton, the gland consists of : — 



(1) A terminal coiled secretory portion, which is wider than 



the rest of the tube. 



(2) A coiled duct leading from this to the base of an epithelial 



downgrowth of the general epidermis. 



(3) An intra-epidermal portion, pursuing a winding and 



irregular course through the core of the epithelial 

 downgrowth, to open on the surface. 



Poulton describes the secretory portion of the tubule as being 

 " lined with short columnar cells surrounded by a longitudinal 

 layer of smooth muscle-cells," and in his fig. 8, Plate xiv., outlines 

 these latter with great distinctness. AVe do not think that the 

 words " short columnar cells " well express the appearances seen 

 by us in a large number of specimens from different animals. The 

 cells lining this part of the duct are rather large and granular, 

 with nuclei which stain well with oi'dinary nuclear stains, but the 

 protoplasm very slightly or not at all. These cells surround a 

 wide lumen and rest upon a basement membrane, between which 

 and the secretory epithelium small triangular strongly staining 

 cells are intercalated at intervals. The whole is surrounded by a 

 sheath of fibrous tissue, but nowhere have we been able to find 

 any trace of fusiform or muscle cells (fig. 3). 



The character and arrangement of the epithelial cells in this 

 secretory end of the duct somewhat suggest the appearance of a 

 transverse section of the alveoli of a mucous salivary gland in 

 mammals. 



The duct leading from the secretory portion of the tube to the 

 epidermal downgrowth consists of two layers of cells. An outer 

 circle of short columnar cells, which exhibit a faint striation. 



