118 Mr. O. H. Latter on the Prothoracice Gland of 
Jackson for very kindly furnishing me with an abstract 
of these memoirs. 
Rengger (16), writing in 1817, incorrectly asserts 
that the gland discharges its secretion by means of two 
eversible muscular tubes, from which the secretion is 
ejected. 
Von Siebold (20), in 1848, mentions that the larva 
can defend itself by discharges of a corrosive liquid. 
I can find no further contribution of any importance 
before that of Klemensiewicz (8), 1882. This author 
gives a very full and, in the main, accurate account and 
figures of the structures, and suggests that the secretion 
is formic rather than acetic acid; at the same time, he 
rightly assigns the actual discharge to the action of the 
muscles of the body-wall. 
Poulton (12), 1886, proved the acid to be formic acid, 
but erroneously described the eversible processes. In 
1887 (18) this error was corrected by him, but, as pointed 
out by Schiiffer (18) and (19), he only described the external 
appearances, and thus fell into the error of regarding the 
median sac as a storage organ ; whereas the true sac is 
not eversible, and is the actual secretory gland. ‘lhe 
same author in 1887 (14) and (15) determined the 
strength of the formic acid solution, and proved its pro- 
tective value by experiments on natural foes. 
Since the specimens I have examined, both by dissec- 
tion and series of microscopic sections, exhibit several 
differences to those described by the above authors, I give 
my own results in full. The horizontal slit-like aperture 
which is visible upon the red margin of the prothorax leads 
into a shallow cavity, which I shall refer to as the “ ves- 
tibule.’ This is compressed antero-posteriorly, but of 
slightly greater width than the slit laterally. From nearly 
the right and left corners of the vestibule there pass 
backward and outward (in the retracted condition) a pair 
of hollow tubes capable of eversion. ach tube, after a 
very short course, divides into two main parts, about 
1-3 mm. long when extracted and preserved in alcohol, 
which end blindly (vide Fig. 1, ¢!, #) ; from the point of 
bifurcation a very short third tube is given off (é). Of 
the two tubes the anterior, when everted (#), is slightly 
the longer, and its cavity is divided into two for a very 
short distance at the apex (vide Fig. 6): to the apex of 
this tube is attached a pair of retractor muscles (r.m.!), 
