131 
Typical specimens of A. marina are found in the 
littoral zone. Their burrows are usually U-shaped (see 
below). One end of the burrow is marked by a casting 
and the other by a funnel-shaped hole through which the 
head was probably withdrawn, and through which it may 
be again protruded when the burrow is covered by the rise 
of the tide. The worm is almost invariably found head 
downwards in such a position that the tail and posterior 
part of the body lie in the limb of the burrow connected 
with the casting, while the head and anterior part of the 
body le either in this or in the horizontal limb of the U. 
The worms average about seven to nine inches in length,* 
and their gills, which are best developed in old, deeply- 
pigmented specimens, are composed of nine to eleven 
stems each provided with three to five pairs of short 
lateral branches (fig. 22). These littoral forms breed in 
the spring, usually from the end of February onwards for 
about a month but specimens containing ripe ova may be 
occasionally met with up to the end of April,t and on the 
Lancashire coast even later. The smallest specimens 
found in the sand are 17 mm. in leneth (see below), 
possibly smaller ones are present but have escaped obser- 
vation. Young specimens are pinkish in colour, due to 
the fact that numerous blood-vessels are seen through the 
translucent body-wall, and their gills are usually bright 
* The largest specimens of the littoral variety I have seen, are 
several found near Musselburgh, on the Firth of Forth, measuring 
340 mm. (about 133 inches) in length. 
+ I am inclined to believe that, in some localities at any rate, 
Aremicola marina also breeds about August or September. Large 
specimens were taken near Musselburgh in July, 1903, which contained 
great numbers of ova and sperms in an almost ripe condition. In 
other full-grown specimens from the same area, taken near the end of 
October, not a single large egg or mass of spermatids was to be found. 
Among the specimens examined on both occasions were both littoral 
and Laminarian forms. In others, taken early in January, 1904, 
genital products are small and scarce in the colomic fluid. 
A month later, in males, spermatogonia and spermatids, and in 
females young ova (06 mm. in diam.) are present in quantity. 
