As shown in Plate XXVI a , fig. 9, the feet by-and-by assume a lobate form, and
the bristles lengthen, while two rounded papillae mark the anal cirri. The body is comparatively
broad and short, and the anterior end truncated.
At a stage a little subsequent to the foregoing the head is better differentiated, and
the lateral tentacles appear as two rounded papillae on each side of the median dimple.
There were ten feet in the example, and the scales were well formed. The tentacular
cirri had a single large (the largest in the animal) curved dorsal bristle projecting at the
base, with prominent rows of spines, and one or two smaller bristles just appearing
beyond the surface. The organs themselves showed indications of developing cilia, as
also did the dorsal cirri. Inferiorly the palpi formed two large rounded discs on each
side of the head, projecting laterally, but not yet reaching the front. No trace of a
median tentacle was observed in this specimen. The dorsal bristles were all curved,
with prominent rows of spines, and the tips of the ventral had also very distinct
spinous rows. The bristles project prominently (nectochsete stage). No caudal styles
were present.
In Plate XXVI a , fig. 10, the next stage is represented. The head is less bluntly
conical, and the two tentacular cirri are leaf-shaped, and soon the tip of the powerful
dorsal bristle at their base projects nearly straight outward. The body is more elongated,
the feet more prominent, and the bristles project more than half the diameter of
the body on each side. The caudal cirri are now broadly lanceolate. Minute scales are.
present.
The dorsal bristles resemble the ventral more closely than in the adult. Moreover
they approach those towards the posterior end of the adult rather than the median, a
fact which may be connected with the growth of new segments between those adjoining
the head and the tail. Thus it is that the anterior and posterior segments of the adult
show the primitive condition of the bristles, the most modified and the most typical
being those in the region between them.
In the stage shown in Plate XXVI a , fig. 11, the median tentacle (which may have
been lost in the previous preparation) projects conspicuously in front, and the caudal
cirri with tapered extremities are distinct.
In early stages, in which eight feet and four pairs of scales occur, the eyes on each
side are nearer each other than subsequently, and a smaller third black speck is observed
on each side in front of the rest on the under surface near the site of the adult eye,
though the peaks are not yet formed.
In the stage figured in Plate XXVI a , fig. 12, the head is still further defined, the
eyes being arranged obliquely on each side (the posterior pair nearer each other than the
anterior). The median and lateral tentacles are distinct, and the palpi project prominently
forward, with tapering extremities. Their margins are crenated, but distinct
papillfe were not observed. The tentacular cirri show short clavate cilia. The scales
are larger, and have short clavate papillae projecting from the outer border, the last
pair of scales having the largest cilia. The feet are deeply cleft and prominent, and the
slender shafts of the bristles have become greatly elongated, so that they project far
outwards on each side. There were nine bristled feet in the example. In this instance
TROCHOSPHERE. 325
the caudal cirri were absent (had fallen off), and a distinct papilla occupied the centre
of the caudal region.
When fourteen feet are present a great advance has been made in regard to the
head, cirri, and feet. The head shows a blunt peak on each side, and the median
tentacle is proportionally large and long, while the palpi have not yet attained full
development, though they show the rows of minute papillas. Two large black eyes are
situated posteriorly, and two occur on the mid-lateral region, and are well seen from the
dorsum. A considerable interval occurs between the eyes of each side. All the cirri
have large clavate cilia. The posterior scales show large clavate papillae with palpocils
at the tip. The bristles at this stage are long, but they do not show distinctive
characters, though the attenuate condition of some of the dorsal suggests an approach to
Gattyana (Nychia). The specific identity of those captured in the tow-nets could not,
of course, be absolutely determined.
A different trochophore appears in the nets in June, characterised amongst other
things by its black and brown pigment-belts at the ciliated ring, the former tint
being in front of the latter (Plate XXVI a , fig. 15). This form closely approaches
Dr. Hacker’s species (Taf. iii, fig. 2) from Naples, though certain points of difference
are present.
In this species the tips of the bristles seem to be less elongated, and the pre-oral
lobe is curiously marbled with black pigment. When scales form, the body is marked
in a somewhat tessellated manner, with transverse bars of reddish-brown pigment. At
this stage also the anterior end (ventrally) has two rounded, pigmented, lateral regions,
with a patch of black in the centre. A little later the black pigment bounds a median
central region in front, and there are six eye-spots, two large rounded eyes on each side,
and a black crescentic eye to the outer side of the anterior.
The body is shorter, the feet more closely arranged, and the scales more persistent.
The latter have traces of low papillm on their outer edge, and the surface is roughly
areolated, probably from papillae, as might occur in the young of L. squamatns. When
the bristles are viewed from behind the spikes are alternate. The tips are much shorter
than in the previous form, and the shafts stouter. Large diatoms often occur in the
intestine.
In the stage (Plate XXVI a , f i g : 18) with the developing palpi the head is rounded
in front, and there are often three or four additional eye-spots besides the four normal.
The single spine of the first foot is prominent, and also two curved bristles. A band of
black pigment bounds the anterior border of the snout.
There are eight feet, the dorsal bristles of which present very fine serrations, and
thus differ wholly from the previous forms. The ventral bristles have short tips with
rather closely arranged spinous rows. The caudal end terminates in a pointed pygidium
without cirri. In the early stages the bristles of the first foot are largely developed in
proportion, and must be especially useful in protecting the head, The cirri in this form
present a somewhat ovoid outline.
As soon as the palpi have developed (Plate XXVI a , fig. 19) the head shows a deep
notch in the centre, the two large black eyes on each side being situated far back, the