158 ZOOLOGY 
taria they often correspond in number with the nephridia. 
Their products ripen in the coelomic fluid (Fig. 98), and usually 
escape through the nephridia, 
| they may however escape by 
Vea rupturing the body-wall, Im- 
ah pregnation takes place exter- 
nally. The eggs are sometimes 
laid in small masses of jelly ; 
REE 
4 
a 
ie sometimes they remain under 
\ps the care of the parent, under the 
f ie } elytra in Polynoe, in a cavity in 
1s the operculum in some SER- 
: oe 
PULINAE, and attached to the 
tube amongst the TEREBELLIDAE. 
Asexual reproduction is not 
common ; it occurs, however, in 
the SERPULIDAE and SYLLIDAE. 
In the former family a head 
is formed by one of the seg- 
ments in the middle of the 
Fic. 101.—Parent body, and the animal then 
stock of Autoly- divides just in front of this. 
tus  cornutus. 
After A. Agassiz. In some of the SYLLIDAE, 
Autolytus, for example, one of 
the posterior segments, usually the last, gives 
rise to a new individual; this may be repeated, 
and chains of zooids are formed (Fig. 101). 
These zooids break off, develope generative 
organs, and reproduce sexually. As the original 
worm was without sexual organs, this genus 
exhibits an alternation of generations; a very 
uncommon phenomenon in Chaetopods. It is 
further complicated by sexual dimorphism, the 
i 
sur 
an Db 
ae 
.& \\ 
Wl 
ps 
‘ 
ia 
a 
h 
Ary 
y, 
y 
\ 
Ca 
ee ey, 
=. 
. Css 
BE 
Beas 
Fic. 102.—Wereis 
pelagica, L. 
After Oersted. 
male worm being in many respects different in appearance from 
the female. A somewhat similar phenomenon occurs in Nereis 
(Fig. 102), one form being known as Heteronereis: this genus 
is polymorphic, for in addition to the male and female forms, 
hermaphrodite individuals also occur. 
