210 TRANSACTIONS OF SECTION D. 



3. Phagocytosis and Protozoa. By E. S. Goodrich, F.B.S.* 



The Food of Larval and, Post-larval Fishes. 

 By Dr. Marie V. Lebour.^ 



Further Observations on the Building Habits of the Polychcete Worm, 

 Pectinaria Koreni, Mgr. By Arnold T. Watson, F.L.S. 



The Abstract of a Note by the Author on the Habits and Buildina; Organ of 

 Pectinaria (Lagis) Koreni, Mgr. has appeared in the Report of the Proceedings 

 of Section D. at the meeting of the Association in Birmingham, 1913. 



Since then he has made fvirther observations and experiments, as the result 

 of which he has found that the suction therein mentioned, by means of which 

 sand below the surface is removed by the worm for the purpose of forming 

 working space, rapid burrowing and other purposes (the eand always travelling 

 between the wall of the tube and the dorsal side of the worm) is not the result 

 of ordinary peristaltic action, but is due to two currents through the tube (at 

 opposite sides of the worm) which differ considerably in character, though both 

 are the effect of waves produced by the worm's body. 



The current produced by the dorsal body-wall of the animal, thouarh it is 

 eufficient to draw into the tube the sand sweot to its mouth bv the fflistenins 

 head-bristles, is insufficient to expel it through the small end of the tube ; and 

 for this purpose it is reinforced bv a much more powerful current, for production 

 of which the ventral body-wall is specially adapted. This wall is exceedingly 

 thin and mobile, while the dorsal is very thick, and consequently slower in 

 action. The direction of the waves can be reversed and the worm is evidently 

 mainly dependent upon the ventral one for supply, of water for respiration. In 

 production of the currents as described above the worm is assisted by the 

 alternate extension and retraction of its body. 



Owing to the head nf the worm being always buried under the sand, and to 

 the great number of tentacles which surround the mouth, it is impossible to see 

 the building operations of the adult, but by observation of the post-larval stage 

 (when the tentacles are few, and before the worm has dug itself into the sand) 

 the author has been successful in seeing a portion of a sand-tube actually built 

 and attached to the membranous tube, which at the time of its later metamor- 

 phosis is secreted by the larva. This membranous and characteristic tube is 

 apparently secreted rapidly once for all by the whole surface of the body. It 

 appears to consist of plates of areolated chitin. It is evidently indispensable to 

 the future life of the worm, as apparently, it cannot be replaced, and in its 

 absence iiiot only is it impossible to commence building the permanent tube for 

 want of something to which to attach the sand, but the violent unrestrained action 

 of the ventral body-wall when drawing water through the tube for purpose of 

 respiration occasionally causes splitting up the middle of the back of the young 

 worm. 



In the early post-larval stage there are two buccal tentacles only ; by. these 

 the minute particles ( yTrrrTr to i^jLj inch in size) are collected and passed to the 

 mouth which opens at their base; here, what is required for food is swallowed, 

 but such sand-grains as seem suitable for building purposes are rolled over for 

 a short time in the moutb, and then deposited by it on the edge of the tube at 

 the point selected ; the young worm then advances slightly in its tube and, for 

 four or five seconds, applies to that sand-grain the organ which, in the author's 

 previous note, is called the ' building organ,' but which it is now evident 

 merely supplies the cement from the cement-gland beneath. 



In the adult worm there are numerous tentacles which collect the sand-grains, 

 and in their midst a mobile membranous horse-shoe-shaped organ (not previously 

 recorded by any naturalist), which no doubt (as in Sahellaria) guides the sand 



^ For an account of leucocytes of invertebrates described in this paper, see 

 Quart. Jovrn. Micr. Sci., Vol. 64, Pt. 1, p. 19; Oct. 1919. 



- See Journ. Marine Biological Assoc, Vol. 11, No. 4, May, 1918; Vol. 12, 

 No. 1, July, 1919; remainder to be published in same journal. 



