Preliminary Note on the Eggs and Larvae 
of Arenicola marina L. 
By 
H. Blegvad. 
(Danish Biological Station, Nj^borg.) 
After several unsuccesful attempts I succeeded last year in 
observing the deposition of eggs and in following the early develop- 
mental stages of Arenicola marina in an aquarium in Nyborg. 
On August the 6th I found upon the surface of the sand in which 
some adult Arenicolas lived, a thin, reddish-yellow layer of eggs, 
deposited within a circle of about 20 cm in diameter. The eggs 
rested loose upon the sand, but whirled up like a cloud by the 
slightest movement in the water. One of the eggs is represented 
in Fig. 1 (a); they are discoidal and resemble very nearly, as to 
size and shape, the eggs found in the body cavity of ripe Areni¬ 
colas (see I. H. Ashworth „Arenicola“. Proc. and Trans. Liver¬ 
pool Biol. Soc. Vol. XVIII. 1904, Fig. 68). — On the same day 
some of the eggs were found in the first stage of cleavage (b), 
and the next day some of them reached the morula stage (c_d). 
On August the lOth the first larvae (e), 0,207 mm long, were 
hatched and swam actively about in the aquarium by means of 
their cilia; they are telotroch, have two brownish-red eyes and 
long sense-hairs upon the front part of the body. Between the two 
bands of cilia they have a longitudinal band of short cilia on the 
ventral surface. Colour of the body yellowish-white; no setæ. 
Two days later one pair of spatulate setæ (i) appeared; the larva 
(f) is now very nearly like the larva of Arenicola claparedii as 
hatched from artificially fertilized eggs (Ashworth 1. c. Fig. 76). 
On the 14th of the same month another segment acquired its setæ 
(g) , and the chaetigerous segment in front of this now had two 
Vidensk. Medd. fra Dansk nalurh. Foren. Bd. 76. 
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