1899-1900.] Mr Crawford on Rectal Gland of Elasmobranchs. 55 
On the Rectal Gland of the Elasmobranchs. By J. 
Crawford, M.B., C.M. Communicated by Dr Noel Paton. 
(With a Plate.) 
(Read December 4, 1899.) 
(From the Laboratory of the Royal College of Physicians of 
Edinburgh.) 
The so-called rectal gland of Elasmobranch fishes claimed notice 
early in the history of scientific research, as might indeed he ex- 
pected from the obviousness of its appearance and the invariability 
of its occurrence. But, in spite of this fact, the rectal gland 
remains one of those organs the knowledge of the structure of 
which is unsatisfactory, and the conjecture as to the function of 
which is consequently hazy. 
As far as can be ascertained, Professor Monro of Edinburgh 
(the second of that well-known name) gave the earliest descrip- 
tion of the rectal gland in his work upon the Structure and 
Physiology of Fishes, published in 1785. He refers to the organ 
as the “appendix digitif ormis, ” the “appendix vermiformis,” and 
in one place as the “caecum.” Dumeril (4), in Suites a Buffon , 
amplified Monro’s description, and various other writers on zoology 
have taken the subject into consideration, the latest structural 
description being that of Blanchard, published in 1880 (7). 
I have been unable to find any description of the microscopical 
appearances of the structure of specimens prepared by the later 
and more satisfactory methods of investigation, and it seemed 
therefore of interest to make an attempt to elucidate the structure 
by a study of sections prepared by such methods. I shall accord- 
ingly first give a short account of the characteristics observed, and 
afterwards consider briefly the various theories which have been 
advanced regarding the possible function of the organ. 
Macroscopic Appearances. 
To the naked eye the rectal gland presents an appearance 
varying somewhat in the different genera in which it occurs, the 
