978 MR. F. A. POTTS ON 
only segments like themselves when the other two regions have 
been completed. 
Fragments consisting of segments of the posterior region 
alone are, however, occasionally met with, and in one case 
(Table Tl. No. 3) a minute regenerating stump was found. At 
the same time there is no evidence that complete regeneration 
occurs from abdominal segments alone. 
Another case may be mentioned in which autotomy had 
occurred in the middle of the anterior region and a number of 
segments of smaller size were superimposed on the older 
segments. 
Plate V. illustrates two well-marked regeneration stages of the 
anterior region from individuals mentioned above, and they 
should be compared with the individual of normal development 
shown on the same plate (fig. 14). 
REGENERATION IN Cheetopterus. 
Since the above was written, | have read the observations of 
Gravier on autotomy and regeneration in Chetopterus variopedatus. 
When an individual is seized by the anterior part of the body, or 
when it is strongly irritated, rupture takes place between the 
first and second segments of the median region—this being the 
place of least resistance. The anterior fragment can reproduce 
all the rest: the posterior has not always been regarded a 
capable of regeneration. But Gravier (6) describes and | figures a 
posterior fragment, collected at Saint Vaast-la-Hogue, which 
Carries a regenerated anterior region ay differentiated but quite 
minute. Gravier’s drawi ing (l.c. fig. 2, p. 147) resembles almost 
exactly those I have given for P. prolifica. The whole anterior 
region hardly equals in length a single original segment, but it 
possesses a buccal funnel and per istomial tentacles, and the lateral 
border is marked out into segments, 12 conical seta-bearing 
notopodia being present on each side. Only in the 4th segment 
the special sete are not indicated, and the peristomial tentacles 
are unequally developed. There are some irregularities, also, in 
the notopodia, but, generally speaking, they are of nearly equal 
development. Only the last segment is markedly smaller than 
the rest, which thus appear to be marked off nearly simultaneously. 
The total number of segments is 12, while the normal number is 
only 9. Individuals with 12 segments are very exceptional, and 
it is curious to find that in regeneration the maximum number 
of segments should be formed. 
The first segment of the median region is present, but in a 
very rudimentary condition. Noto- and neuropodia are visible, 
but it has obviously been formed after the segments of the 
anterior region. 
If we summarise the phenomenon so far as it is known in 
Chetopterus, it may be said (1) that autotomy occurs sometimes 
