THE STING-RAY. 43^ 



terminate by an orifice which is curiously pigmented, and some 

 sections show the secretion issuing from the tip. 



The number of these secreting filaments varies, and apparently 

 they are provided in order to carry the poison to the tip of the 

 dart, where the glandular tissue no longer is present. The 

 width of a filament is from 2 to 3 mm. 



It should be mentioned that in one spine of the three of 

 which I have sections, there is a well-marked nipple projecting 

 from the central canal near the base (see text-fig. 2), and the 

 canal can be seen surrounded by a layer of muscular fibres. 



A diagram of this arrangement of glandular tissue, central and 

 lateral canals, nipples and secreting filaments, is given in text- 

 fig. 7 ; it is purely diagrammatic, and does not give with any pre- 

 tence of accuracy the actual relative size of the nipples compared 

 with the teeth of the dentate margin. 



In concluding this account of the microscopic anatomy of the 

 spine, I must mention with gratitude the help I have received 

 from Dj'. Stuart McDonald, of the University of Durham, whose 

 laboratory assistant, Mr. Percy Landreth, took the micro- 

 photographs from which several of the illustrations have been 

 prepared, and who gave me much technical heljD. 



I must also mention the kindness of Mr. C. Tate Regan, of the 

 British Museum (Natural Historj^), in looking at my sections, in 

 giving me references to the literature on the subject, and making 

 suggestions as to the form this paper should take. 



I must also thank those members of the Board of Agriculture 

 and Fisheries, including Mr. Borley, for the help they have given 

 me in obtaining specimens. 



In conclusion, I would add that my investigations began in 

 1911, and were undertaken in ignorance of the work of Dr. Porta, 

 who, so far as I can ascertain, was the first to describe the gland 

 of the groove in the spine of Trygon. 



Summary of the evidence that the gland is really a poison- 

 organ : — 



i. That the nature of the wounds produced are not such as 



would happen after a simple laceration ; 

 ii. that the symptoms of acute pain and inflammation are 

 similar to the symptoms produced by the stings of the 

 other venomous fish, particularly the weever ; 

 iii. that the staining reactions of the secretion are similar to 



the staining reactions of the poison of Trachinus draco ; 

 iv. the observations of Dr. Lo Bianco quoted by Dr. Porta. 



The observations of Dr. Lo Bianco are very interesting. He 

 himself saw a young man become extremely pale and fall down 

 almost senseless for a few minutes, from having received only a 

 very small puncture while he was in the act of passing a Trygon 

 weighing 3 kg. from one person to another. Besides which he 

 also relates the following most interesting fact. In the month of 



29* 



