AND HABITS OF THE AMMOCHARIDA. 235 
The entire nervous system is fully described by von Drasche 
(12. p. 13), who observes that it is very rudimentary in character, 
and lies outside the muscular layer near the surface of the 
epidermis. 
It may be asked whether the localization of the coloration 
over the nervous system may not be connected with the animal’s 
sensitiveness to light? Some of my sections seem to suggest 
the possibility, but at present this must remain undetermined. 
I am able to show that a special function is performed by the 
triangular ventral area (v.a., Pl. 25. fig. 20) bounded by the two 
lines which descend from the “ eye-spot.” The body-wall is at 
this point very much thinner than that of adjoiming parts, and 
modified, as I shall show more fully, in relation to the building- 
habits of the animal. 
The structure of the creature is remarkable in many other 
respects, and for minute anatomical descriptions reference 
should be made to the papers of Claparéde, von Drasche, 
Gilson, and Ogneff. Speaking generally, I may point out that 
a cuticular covering to the epidermis is absent, except on the 
anterior portion of the body; that the underlying circular 
muscles are limited to the “thoracic” region; and that the 
longitudinal muscles, which are exceptionally powerful, form 
throughout its entire length an inner lining for the body-cavity — 
a layer which is continuous except where it is interrupted by the 
dorsal and ventral mesenteries of the alimentary canal. These 
powerful muscles impart considerable rigidity to the fore part of 
the body ; a feature which gradually disappears posteriorly, the 
thickness of the muscular layer in that part being greatly 
reduced. According to Gilson (30. p. 95) there are no peritoneal 
parietes distinct from the longitudinal muscular layer, his view 
being that these two layers are replaced by one musculo- 
glandular layer which, amongst other things, is excretory in 
function. This view is, however, opposed by the observations 
of von Drasche (12. p. 20) and Ogneff (32.). 
A striking and characteristic feature of the Ammocharida, 
which has from the first attracted the attention of naturalists, 
is the existence in the anterior segments of peculiar, very long, 
cylindrical, rigid glands (¢.g., Pl. 28. fig. 6) of considerable calibre 
which hang loosely in the body-cavity. Hach is attached to the 
body-wall by one extremity which, greatly reduced in diameter, 
forms a minute duct running through the body-wall, opening 
