Neanthes caudata — Reish 
221 
harbor. One specimen with 18 setigerous seg- 
ments was taken in a plankton tow on Oc- 
tober 21, 1954, in Los Angeles inner harbor. 
Further appearance of segments is indicated 
in Table 2. 
The tentacles and first pair of peristomial 
tentacles appear as small knobs on the ninth 
day. The next two pairs of peristomial ten- 
tacles arise in the next two days (Fig. 5 ). The 
fourth pair was slow to appear; it did not 
form until the larva was 23 days of age and 
possessed 24 segments. The palpi were seen 
first at 10 days (Fig. 5) and became biarti- 
culated a few days later. 
The jaws were noticed when the larvae were 
10 days old. They were colorless structures 
and consisted of only the terminal tooth. The 
first lateral tooth was added by the next day. 
Additional lateral teeth were formed rapidly; 
a larva 21 days old had 7 teeth. The tips of 
the jaws became dark brown at this time. 
Lateral movements of the jaws did not occur 
; f ■ • ' ' ' • 
Fig. 4. Photomicrograph of a three-segmented larva 
of eight days in age. The anal cirri are beginning to 
develop as small knobs at the right side of the figure. 
Length, 750 /x. 
until the larvae had 15 segments, or just prior 
to leaving the parent tube. 
Paragnaths were seen first on the maxillary 
ring at 14 days; they did not appear on the 
oral ring until 21 days. The paragnaths be- 
came dark brown at about 26 days when the 
animals possessed 32 segments. Figure 9 is a 
photomicrograph of the paragnaths of area I. 
A total of 37 paragnaths was observed in this 
specimen, which was a typical number for 
young worms. Adult worms reared in the 
laboratory had from 12 to 16 paragnaths pres- 
ent, indicating a loss in number with age. 
This was contrary to what was observed by 
the author (1954) in Nereis grubei , which 
showed little change, if any, with age. 
Fig. 5. Photomicrograph of five-setigerous seg- 
mented larva 10 days old. Shown in formation (from 
left to right) are the tentacles, palpi, two pairs of peris- 
tomial tentacles, five setigerous segments, four seg- 
ments without setae, and one pair of anal cirri. Length, 
1.1 mm. 
The development of N. caudata collected 
at Cherbourg, France (Herpin, 1926), and 
Los Angeles Harbor, California, does not 
differ in morphological details, only in regard 
to time of appearance of structures. The three 
larval setigerous segments arose a day earlier 
at Cherbourg. This difference in one day con- 
tinued until about 10 to 11 days when larvae 
from both localities possessed six larval seg- 
ments. However, in the Los Angeles Harbor 
