POLYCH.ETA FROM THE N.E, PACIFIC. 985 
no but doubt that the tubes are connected. Usually each con- 
stituent tube contains a single individual longer than those of 
P. proiifica, Small subsidiary apertures may be placed at the end 
of branchlets of the main tube, as in P. prolifica. 
These distinctions which I have attempted to draw may, on 
further examination of the genus, prove to be insufficiently 
grounded. I feel quite certain, however, that P. prolifica in the 
N.E. Pacific does not usually form the dense colonies charac- 
teristic of P. socialis, nor do connected tubes run parallel as in 
P. anglica. 
It is possible, too, that these three species differ in the extent 
to which asexual reproduction is developed in each. In particular, 
it may be mentioned that P. prolifica is the only species in which 
asexual reproduction was found to be proceeding at the moment 
of discovery.* In P. anglica I was not successful in finding any 
example which showed signs of recent regeneration. It is 
probable that this phenomen takes place later in the year than 
the time when my specimens were collected, but I incline te 
beheve that autotomy and regeneration are never so frequent as 
in P. prolifica, a cvcumstance which accounts for the smallei 
number of individuals contained in much longer tubes. 
In the morphological characters of the animals themselves, I 
must confess to a considerable difficulty in distinguishing between 
these three species. Myr. Crossland has pointed out that some 
species of Phyllochcetopterus are easily recognised by definite 
characters, like the number of inodified sete in the notopodium of 
the fourth setigerous segment, the presence or absence of eye- 
spots, and the number of sete in the notopodium of the 
posterior region (C), as well as the character of the tubes. In all 
four species, which have developed asexual reproduction, eye-spots 
are present, a single strengthened seta is usually found in the 
notopodium of the fourth segment and a single seta in each 
notopodium of region C, while the tubes they inhabit are 
creeping and branched. It seems to me that there is sufficient 
difference between the forms here described to preserve them as 
distinct species, though they must, from their morphological 
character's, as well as from their manner of life and reproduction, 
be classed as very nearly related. There are, moreover, differences 
in the size, the number of segments in the several regions of the 
body, and in the shape of the prostomium and peristomium 
which help to supplement the biological peculiarities which I 
have indicated above. 
Comparison of the external Morphology of those Species of 
Phyllochetopterus which form True Colonies. 
(1) The Prostomium and Peristomium.—In P. anglica, the 
prostomium (text-fig. 9) is rather broad, though small, and its 
borders are marked by a line of dark pigment. The eyes ave 
placed on the extreme side of the head, and are overlapped and 
* This was in the summer (May-July). 
