Neanthes caudata — Reish 
217 
favored because of the greater ease in observ- 
ing the animal. The water in the petri dishes 
was changed at irregular intervals, usually 
once every two or three weeks. 
Since the male incubates the fertilized eggs 
and larvae (Herpin, 1926), the developing 
worms were left undisturbed with the male 
until the larvae abandoned the parent tube. 
At this stage the larvae could be pipetted into 
separate petri dishes containing Enteromorpha 
sp. At first many larvae could be placed within 
the same dish, but as the worms grew they 
became cannibalistic and had to be separated. 
A second method (Reish, 1953), but not 
as successful, was to place the bottom half of 
the petri dish containing a male and develop- 
ing larvae into a one gallon aquarium. One 
liter of sea water was placed in the aquarium; 
the water was aerated by an aquarium stone 
connected to a compressed air system. Dried, 
ground Enteromorpha sp. was added twice a 
week. This technique was particularly useful 
for maintaining small larvae for a short period 
of time. 
The Fighting Reaction 
The sexes cannot be distinguished morpho- 
logically prior to the onset of sexual maturity. 
Females may be separated from immature 
females or males by the presence of develop- 
ing ova in the coelom. Only by studying the 
reactions of sexually unknown specimens to 
known males or females could the males be 
distinguished. Herpin (1923; 1926) found 
that a female would readily accept a male but 
would fight off the introduction of a second 
female. These observations were confirmed by 
the author. Not only was it found that females 
would fight one another, but also a similar 
response occurred when two males were 
placed together. This behavior, which is 
termed the fighting reaction, is so definite 
that it was utilized to differentiate the sexes. 
The fighting reaction is most pronounced 
when two worms of the same sex meet di- 
rectly. Each proboscis is everted and the jaws 
extended to grasp the opposing animal. One 
such encounter lasts only a few seconds, but 
successive encounters may extend over an 
interval of several minutes. Termination of 
these fighting periods occurred when the 
worms became separated a few centimeters 
from one another. When one animal came in 
contact with any portion of the body of the 
second one other than its anterior end, it 
extended its jaws and attempted to grasp the 
worm. No injuries have been actually seen 
inflicted by this fighting, but when similar 
sized worms of the same sex were left together 
for a day, wounds were observed the next day. 
One or both of the animals lacked its pos- 
terior end, the remains of which appeared in 
fecal pellets. If the two worms were of the 
same sex but differed in size and were left 
together for a day, the larger worm usually 
will have eaten the smaller by the next day. 
This fighting reaction may account for the 
difficulty of culturing several worms within 
the same petri dish as discussed above. 
A modification of this fighting reaction was 
observed in the male following egg-laying by 
the female. A male incubating eggs will fre- 
quently eat the spent female. A spent female 
will fight with a second female that has not 
yet laid her eggs. A male incubating eggs will 
fight with worms of either sex. After com- 
pletion of the incubation period, the male will 
no longer fight with a female. 
The basic behavior pattern appears to be an 
attraction to members of the opposite sex and 
a fighting reaction to members of the same 
sex. This pattern is altered in the male while 
incubating ova; he fights either sex. This 
behavior difference during the incubation pe- 
riod is apparently due to the presence of the 
eggs, although it was not the subject of any 
special investigation. Apparently there is no 
change in the behavior of the female during 
its life cycle. 
Incubation of eggs is known to occur in 
Micronereis variegata (Rullier, 1954), M. na- 
naimoensis (Berkeley and Berkeley, 1953), 
Platynereis massiliensis (Hauenschild, 1951), 
Laeonereis glauca (Herpin, 1929), and Cera - 
