198 Mr Potts, The Swarming of Odontosyllis. ' 
spermatozoa of that species was very brief and that fertilisation 
must take place very shortly after dehiscence, while probably in 
O. gibba and O. ctenostoma the genital products can survive for — 
a much longer time in sea-water. 
In the literature of swarming amongst Annelids a majority of | 
the observations refer to the genus Nereis and show a great 
diversity of reproductive habits. Hempelmann*, who has in-— 
vestigated the case of NV. dumerilii very thoroughly, found that — 
at Naples heteronereid forms occurred at the surface of the sea 
from Ist October, 1908—15th May, 1909. From 15th May, 
1909—15th August, 1909 there were no heteronereids. The 
mature worms appear at the surface indifferently in the day or 
the night and usually occur not as swarms but scattered in- 
dividuals which discharge their eggs or spermatozoa when no 
other heteronereid is near. But on one occasion at least, on 
May 2nd, 1908, there was seen in the Bay of Naples a great 
swarm of NV. dumerilia and NV. coccinea. 
Similarly attention has been lavished on the heteronereids 
which are seen off the east coast of England. Sorby+t was 
accustomed to observe the phenomena in the summer throughout | 
a long series of years. On several occasions he saw immense 
numbers of heteronereids on the surface. The date, time and 
place of occasion of these are indicated in the following table :— 
23 May, 1885. N. dumerilu. In the evening at the | 
mouth of the Colne. 
16 July, 1898. A bs At 5 o'clock in the morn- ‘| 
ing at the mouth of 
the Stour and Orwell, 
the sea being covered 
with millions of worms, | 
11 May, 1882. NV. longissima. In the evening near Sheer- | 
ness. 
24 May, 1889. . 7 At the mouth of the. 
Orwell. 
9 September, 1889. a - In the evening at Queen- | 
borough. 
In twenty years Sorby only saw five such great swarms of 
nereids. He does not state that he ever observed isolated hetero-— 
nereids on the surface of the sea, and for this reason the record — 
of these English occurrences is lamentably incomplete. But his | 
observations go to establish several facts which Hempelmann’s more | 
thorough, but less extended, investigations give no clue to, viz.:— — 
* « Zur Naturgeschichte von Nereis dumerilii,” Zoologica, Bd. xxv. Heft 62, 1911, 
pp. 92 ff. 
+ Sorby, Journ. Linn. Soc., London, vol. xx1x. 1906. 
