The poison gland of trygon.—Supplementary note

Abstract

In a recent communication on the Defensive Spines of Fishes, published in the Philosophical Transactions (Series B, vol. 212), I described the glandular structure in the lateral groove of the caudal spine of Trygon ; and on p. 7 I gave a drawing of a transverse section of the distal portion of the spine, showing lateral processes or projections which appeared to overlap a space containing isolated masses of epithelial cells. The suggestion was made that these lateral flaps of tissue were intended to protect the glandular epithelium in that part of the spine which did not lie in contact with the opposing tail. But it was pointed out that sections showing the epithelium completely filling the space beneath the processes were wanting, and it seemed necessary for the completion of this research that sections should be obtained confirming this point. Through the kindness of Mr. Thomas More, of the Sungei Bulch Estate, Kuala Selangor, Federated Malay States, I received, in very good condition, three small ikan pari in June, 1923. According to Gimlette, in his book Malay Poisons and Charm Cures (p. 117), is the native Malay name for fish, and pari is used collectively for the sting rays, eagle rays and electric rays. The specimens I received were those of the sting ray ( Sengat pari ), and after six months of careful decalcification the spines were ready to imbed and examine. The result of an examination of the sections confirmed the observations I had previously made on the special epithelial structure found in the lateral grooves near the base of the spine, and very fortunately, sections of the distal portion of one of the spines provided a complete picture of the tissue in the groove. These sections, as the accompanying figures will make clear, confirm my supposition as to the function of the lateral processes; the glandular tissue and small masses of secretion are seen completely filling the space which in previous sections only contained isolated groups of cells and secretion. Where the extremities of the processes meet, there is a small space through which portions of coagulated secretion have passed. The secreting cells have been caught in an active state, as in the cell mass are to be seen complete cells, some distended with secretion and others in which only the remnants of a nucleus remain; in fact, all stages of the secreting process can be observed.