YELLOW-BROWN CELLS OF CONVOLUTA PARADOXA. 433 
tion and partly by bristle-like pegs, which stand out from 
the delicate cilia with which the body is clothed, and which 
are more numerous in the posterior region. Thus fixed, the 
anterior end is reared up caterpillar-wise, and the ventral 
surface fitted again to the substratum, or, quitting the sub- 
stratum, the animal may swim freely in the water. 
Though by no means gregarious like C. roscoffensis, C. 
paradoxa may be taken in fair quantity by following down 
the big tides and washing the finer weeds which it chiefly 
affects into a white porcelain dish, or by collecting the weeds, 
bringing them into the laboratory, taking them piece by 
piece and holding them so that the water drains down from 
them into a white dish. The animals follow the water 
draining from the weed, and so collect in the dish below. A 
particularly good catch may result in the collection of a 
hundred or more specimens. ‘It is advisable to follow the 
falling tide, since many of the animals desert the weed as the 
tide falls off it, whilst those that remain cling so obstinately 
to the weed that even vigorous shaking fails to dislodge them. 
A white dish is better for the purpose than a transparent 
glass vessel, since C. paradoxa is much more easily 
pipetted off from the former than from the latter. 
The sequence of sea-weeds on the rocks at Trégastel 
proceeding toward the sea is:—Pelvetia: Fucus, with a fine 
yellow-brown epiphytic algal flora attached to the fronds of 
Fucus on the seaward side; Ascophyllum: Himanthalia, 
the long strands of which, only exposed at fairly low tides, 
are also clothed toward their extremities with finer brown 
and dull red weeds; and, in the deep water, rarely and then 
~ but partially exposed, Pycnophycus, whose rounded thallus 
is covered with delicate red weeds, the chief of which are 
species of Ceramium and Rhodomela. 
The limits of the Paradoxa zone are, on the lend’ side, 
the lower edge of the Fucus zone, and, on the seaward side, 
a little before the line which marks the permanently sub- 
merged part of the Pycnophycus formation. Within this 
zone the distribution of C. paradoxa varies with the phase 
