AND HABITS OF THE AMMOCHARIDZ. 231 
and thereby making the later portion of my paper more intel- 
ligible. 
The body of the animal is cylindrical, and especially rigid in 
the anterior portion. It consists of from twenty to twenty-seven 
segments (Pl. 25. fig. 20), and varies in length from about 
30 mm. in the English to 90 mm. in the Italian species. The 
diameter at the anterior end measures from 1 mm. to 3 mm. 
The cephalic segment is slightly swollen and bears a crown of 
flat, laciniated, tentacular branchie, six in number (0.¢., Pl. 23. 
figs. 1, 2 & 3) (three on either side of the body), which are ciliated 
on the inner surface. ‘These are absent in the youngest speci- 
mens, the mouth being then surrounded only by a funnel-shaped 
lip, which is quite entire except for a ventral notch. The processes 
first appear short and squarish in form, with a slight indent on 
the upper edge, which gives the margin a castellated appearance. 
In fully-grown living specimens their height somewhat exceeds 
the diameter of the cephalic segment, but in preserved animals it 
is slightly less. Each process has a wide, very flat base, giving 
rise to three or four branches, which are subdivided into seven 
or more twigs, each terminated by two small rounded mucus- 
secreting lobes. The crown and branchial processes are well 
supplied with coelomic fluid; and in the living specimens the 
latter have, under favourable illumination, a beautiful appear- 
ance, due to the branches from the dorsal blood-vessel and to 
the network of capillaries with which they are furnished. In 
British specimens the processes, viewed by transmitted light, 
are semitransparent, pale greenish blue, or yellow, and tinted 
with red; whilst those from Naples are blood-red and in parts 
coloured with a reddish-brown pigment. In cross-section the 
branchiz are somewhat horseshoe-shaped, the concave side 
directed towards the mouth. They are divided into two lateral 
groups dorsally by a crescent-shaped lobe (c./., Pl. 23. fig. 2), 
which is figured and described by von Drasche (12. p. 13) as the 
head containing the brain. This organ possesses another inter- 
esting feature, which seems to have escaped his notice. From 
his admirable drawings (12. pl. i. fig. 3), it would appear that 
the inner wall of the lobe is in unbroken continuity with the 
ectoderm. Favourable sections, however, clearly show that this 
is not the case, and that for a short distance at the apex of the 
erescent the inner wall is entirely separated from the outer 
body-wall and forms a kind of ciliated upper lip, which, by 
