Poly dor a nuchalis — Wood wick 
123 
P. nuchalis. Larvae leave the egg capsules after 
having fed on nurse eggs until the 9- to 12- 
segment stage ( Plate I 5 Fig. 1 ) . Further studies, 
to be reported in another paper, suggest that 
male and female do not copulate as such; a 
reciprocal transfer of sperm involving two pro- 
tandric males occurs. The stored sperm fertilize 
the eggs which develop in the later female stage 
of protandry in each individual. Protandry and 
also neoteny have been reported for Polydora 
hermaphroditica Hannerz (1956). 
Polydora nuchalis does, however, follow rather 
closely the composite life history in the remain- 
ing development. The larval stages described 
below are not unlike those figured for other 
species of Polydora. 
EARLY DEVELOPMENTAL STAGES OF 
Polydora nuchalis 
Egg. (Plate I, Fig. 2.) The eggs are round 
and about 120 g in diameter. They include a 
central mass of light pink yolk granules and a 
very narrow peripheral region which is trans- 
parent. The yolk granules described here appear 
in the gut of all the developing stages up to at 
least 10 segments and are useful in determining 
the developmental boundaries of the gut in all 
these stages. 
Cleavage of the egg is total but unequal as 
has been reported for other polydorids. 
Early Larva, 18 Hours. (Plate I, Fig. 3.) The 
larva, 180 fx long, is transparent anteriorly, the 
yolk granules being concentrated in the pos- 
terior half. The primordia of the peristomium 
and prostomium are set off by ridges. This stage 
has an unusual anteroventral prolongation of 
the larval body. The prolongation was noted 
in more than one series of larvae but no sug- 
gestion can be made here as to its significance. 
It may be abnormal, but its repeated appearance 
and the fact that larvae of this kind continued 
to develop in a normal fashion later have led to 
its inclusion to allow comparison with possible 
future investigations on this and other species. 
The prototroch is located on the ventrolateral 
surface near the junction of the main body of 
the larva and the anteroventral prolongation. 
The telotroch has appeared also but is lacking 
from a wide dorsal portion. 
Early Larva, 36 Hours. ( Plate I, Fig. 4. ) The 
anteroventral prolongation is no longer present 
in this stage and the larva measures only 120 fx 
in length. The anterior part of the larva remains 
transparent; the posterior part is filled with yolk 
granules. The prototroch, not apparent in this 
figure, is limited mainly to the ventral region. 
The formation of the vestibule and the anterior 
portion of the gut has been initiated. 
Late Presegment Larva, 72 Hours. (Plate I, 
Fig. 5.) The larva has elongated and does not 
so closely resemble the egg as did the two pre- 
ceding larval stages. The larva is about 200 /x 
long, nearly double the length of the preceding 
stage; however, it has no true segments as yet. 
The anterior and the posterior body regions are 
transparent with the yolk present in the central 
region serving as an excellent indicator of the 
intestinal portion of the digestive tract. The 
transparency of the posterior region is a result 
of the development of the pygidium. The telo- 
troch is well developed and prominent. The 
prototroch is present laterally, just posterior to 
the two eyes. The lateral eyes are the first pig- 
ment areas to be formed. Differentiation of the 
head and body has begun. 
Early Two-Segment Larva, Five Days. This 
larva, 0.26 mm. long, has two complete segments 
and the beginning of a third pair of setal sacs. 
Two pairs of eyes are now present in the trans- 
parent anterior region. The palpi are beginning 
to bud laterally just posterior to the eyes. The 
development of the vestibule has continued; the 
mouth proper is visible. The posterior gut has 
begun to invaginate but has not joined the 
central concentration of yolk granules. The 
pygidium is set off from the rest of the body 
by a depression in the body surface which con- 
tains the base of the cilia of the telotroch. The 
first pair of dorsal melanophores is located on 
the primordia of the third segment. 
Three-Segment Larva, Six Days. (Plate II, 
Fig. 1.) The larva, 0.30 mm. long, has three 
well-developed segments. It is transparent ex- 
cept for segments two and three in which the 
gut contains yolk granules. 
The palpi have thickened but have not elon- 
gated. The protroch and telotroch are as de- 
scribed for the previous stage. The pygidium 
is cone-shaped and papillated; its appearance is 
