368 POMATOCERUS TRIQUETER. 
of these hooks in each row is great, and in some they are indicated by a dark line with a 
dark speck at the ventral end. 
The posterior hooks (Plate CXXXI, fig. 7d) are smaller, have only seven teeth above 
the modified main fang, but their shape agrees with that of the anterior hooks. Both these 
and the anterior hooks are situated near the edges of muscular lamelle—a provision probably 
enabling them to fix on the walls of the tube with greater accuracy. 
A variety which occurs abundantly at North Uist and is characterised by the sharp 
spike over the aperture of the tube, and almost invariably a three-pronged operculum, has 
hooks which deviate from those at St. Andrews, for they form a long triangle and have a 
larger number of teeth above the modified main fang, viz., eight in the anterior hooks 
and nine or ten in the posterior. A similar spike over the aperture is met with at 
St. Andrews. 
Habits —The species has great vitality, surviving in impure water, or living in a small 
quantity of unchanged sea-water for a week. An example from St. Andrews reached Perth 
on the 14th February, and lived till it was preserved, on July 3rd, in a jug of sea-water— 
meanwhile having made a considerable addition to its tube, the new portion being dis- 
tinguished by its pure white colour. The rapid growth of the tube and the corresponding 
development of the annelid is sufficiently shown by the presence of well-developed examples 
on the carapace of the adult Carcinus manas. Orton! indeed (1914) found that it grew to 
nearly full size in four months, and at this age yielded practically 100 per cent. of embryos 
on being artificially fertilized. 
Reproduction —‘‘ The abdomen is red in the females, and whitish in the males when 
sexually mature ” (Cunningham and Ramage). McBride’ mentions having reared the young 
of fPomatocerus until the larvee attained the adult condition and had formed tubes which 
were attached to the sides of the vessel. Lo Bianco (1909) found those at Naples sexually 
mature in March and April. 
The tube is somewhat triangular in section, with a dorsal keel, and it is firmly fixed to 
shells, stones, rocks and various structures. At Lochmaddy, North Uist, the tubes of this 
form are common at low water under stones, and in turning these over the sharp spike above 
the aperture wounds the hands. Such spikes are less common and less acute at St. Andrews. 
Montagu observed that one on a glass bottle was unusually spread at the base, as if it was 
requisite to take a firm hold of so smooth a surface. Oyster shells in Loch Carron (J. G. J.) 
are often covered by a dense incrustation of this species on both surfaces, and so in the South 
of England—indeed wherever oysters occur. In the same way empty Buccina and other 
shells are densely coated externally and internally, and masses form on various structures 
thrown into the sea on favourable ground. 
Arnold Watson forwarded tubes collected in Wales in which a calcareous grating had 
been secreted inside the fractured posterior end. This as well as the secretion of one-eighth 
of an inch of new tube was done in a fortnight. The accompanying sketch (Fig. 168) by 
Mr. Watson indicates this interesting feature, which he associates with the physiology of the 
parts, especially as he noticed a ‘‘ pumping action of the tail.” The same author has drawn 
attention to the camerated condition of the tubes in many cases—a condition alluded to by 
1 “Journ. M. B. A., vol. x, p. 316. 
2 “Nature, August 10th, 1911. 
