244, MR. A. T. WATSON ON THE STRUCTURE 
combined with a wonderful special arrangement, next to be 
described, has been brought within reach. I have called atten- 
tion to the fact (antea, p. 235) that a small portion of the body- 
wall, represented by a ventral triangular area (v.a., Pl. 25. fig. 20) 
just above the cesophageal ganglion, is very considerably reduced 
in thickness. The object of this is now apparent. Simulta- 
neously with the protrusion of the “ Lippen-organ,” the circular 
muscles (¢.m., Pl. 28. fig. 1) of the lower part of the ‘“ thoracic” 
segment contract, the powerful septal valves (¢.v., Pl. 23. fig. 1) 
are doubtless brought into action, and by means of the imprisoned 
coelomic fluid a very marked swelling of the anterior part of that 
segment occurs, especially in the area above referred to, with the 
result that, at the very edge of the “ thorax,” a projecting pouch 
(¢.p., Pl. 23. fig. 1) is produced. It will be borne in mind that 
the tube (m.t.) tightly invests the ‘“ thorax,” as with a skin, and 
as it consequently covers the pouch, it assumes its form; and 
frcm this it may be realized that the lobes of the “‘ Lippen-organ ” 
(Z.0., Pl. 23. fig. 1), on beg protruded, find themselves pretty 
nearly on a level with the curved upper covering of the pouch. 
By a muscular action of the upper surface of the “ Lippen- 
organ,” assisted by occasional little pushes from behind, the 
fragment (fs., Pl. 23. fig. 1) now commences to travel, sliding 
along smoothly towards the outer lobes of this, whilst the 
epidermis on the underside of this end of it is forced upwards 
and made to take an active part in transferring and affixing the 
fragment, at a tangent (Pl. 23. fig. 1), to the curved upper 
covering of the pouch. This done, the ‘‘ Lippen-organ” is 
retracted into the vestibule, the ‘“‘ thoracic”? muscles are relaxed, 
the pouch disappears, and the parts resume their ordinary aspect ; 
but the fragment just added will be found standing vertically, 
with its base in the required position, and the lower end of its 
inner side firmly attached to the elastic conical sheath. It is 
certain that the cement for this purpose is supplied by the 
‘‘ Lippen-organ,” which must consequently be regarded as a 
glandular structure. 
From my observations of the habits of the animal, I have no 
doubt that the external thickening of the membranous sheath is 
also due to the secretion of this organ, and not, as has been 
supposed, of the thread-glands. The “ Lippen-organ,” which is 
seen in situ in the longitudinal section of the “ thorax” (/.0., 
Pl. 24. fig. 7), is beautifully figured by its discoverer, von 
