PROCERASTEA HALLEZIANA. 463 
PROCERASTEA Hatimziana, Malaquin. Plate CXXXV, fig. 3—head and anterior region ; 
fig. 3a—bristles. 
Specific Characters.—Proboscis forming a cylinder, longer than in P. nematodes, Langer- 
hans. Trepan (proboscis) armed with twenty to twenty-two teeth. Segments forty to 
forty-two previous to reproduction, fifty-four to fifty-six immediately before the appearance 
of the head of the stolon. Coloration uniform light brown. Bristles are compound, 
terminal process short or awl-shaped, or simple bifid with terminal thickenings. Re- 
producing by stolons with long cirri. Lives in interior of tests of Tunicates (Ciona) amongst 
Hydroids and Polyzoa. 
SYNONYMS. 
1893. Procerastea Halleziana, Malaquin. Rech. Syllid., p. 81, pl. xi, figs. 1—14, and pl. viii, fig. 26. 
1911. 9% 5 Potts. Ergebnisse u. Fortschrit. Zool., p. 30, text-fig. 10. 
1915. es 3 Allen. Journ. M. B. A., n.s., vol. x, p. 606. 
1921. ra - McIntosh. Ann. Nat. Hist., ser. 9, vol. vin, p. 309. 
Six specimens were procured amidst Ascidians from a raft moored in Cawsand Bay, 
Plymouth, in September (Allen). 
_ The head and anterior region are shown in Plate CXXXV, fig. 3, and the tips of the 
bristles in fig. 3a, after Malaquin, no example having been available. 
A brief, but excellent, summary of the stolonization of this form is given by Mr. F. 
Potts,! along with other types of reproduction in the Syllids. In Procerastea Halleziana, as 
shown by Malaquin, the twelve to sixteen new segments are intercalated in the middle of 
the stock, and not at the posterior end as usual in the Syllids. Thus there may be in front 
twenty to twenty-two original segments, fourteen to sixteen of recent formation, and then 
eighteen to twenty or more of the original stock, the middle showimg the more advanced 
development of the foot. The head of the stolon is formed on the fourteenth segment. 
The parts soon assume the condition of the adult. 
Dr. Allen? observes (1921) that Procerastea Halleziana was found at Plymouth living 
in membranous tubes on the stems of the hydroid Syncoryne. It was observed to feed by 
piercing the body-wall of the hydranths with its extruded pharynx and pumping out the 
contents of the gastral cavity of the hydroid. The proventriculus of the worm functions 
as a quick-acting pump, making from 150 to 200 pulsations a minute. 
Sexual reproduction in Procerastea is quite similar to that in Aufolytus, each individual 
forming a single large stolon (with stolon-head on segment 14), which is set free as a male 
Polybostrichus or a female Sacconereis, before a second stolon is produced. 
In addition to sexual reproduction, Procerastea was found to be undergoing rapid 
multiplication by a process of asexual reproduction, consisting of fragmentation, followed 
by the regeneration of anterior and posterior ends. 
Fragmentation can be induced by artificial means, and takes place in a definite way. 
The head and first seven setigerous segments form the first piece. This is followed by three 
1 <Spengel’s Ergebnisse und Fortschritte Zoologie, Bd. ii, p. 30. 
* “Philos. T'rans., ser. B, vol. ccexi, p. 131. 
