4 Memoir Sears Foundation for Marine Research 



angles, and the space between the latter forming its base, which is also the floor of the atrial 

 chamber. 



There is a rather conspicuous pigment spot at the anterior end of the nerve cord, 

 which has been called an eye spot or median eye, but which appears not to be a light re- 

 ceptor. Also, an olfactory function has been ascribed to a small diverticulum from the 

 cerebral vesicle, but it is doubtful whether this is correct. 



Habits. Lancelets spend most of the time buried in the sand, in an oblique position, 

 with the anterior end alone protruding.' If removed from the sand they swim actively, 

 bending the body from side to side with a sinuous eel-like motion} it is with this same 

 motion that they bore into the sand, which they do very rapidly. In most cases they burrow 

 tail foremost, but they have been seen to do this with the anterior end foremost, in which 

 case they then assume a U-contour to bring the anterior end out again from the sand. It 

 seems that adults of the genus Branchiostoma seldom emerge spontaneously from the 

 sand, or only for very brief periods, except at spawning time, for we find no record of their 

 capture in tow nets.* But Asymmetron has been so taken (p. 21 ). 



It has long been known that they feed on microscopic organisms which they strain out 

 from the current of water that is drawn in through the mouth and driven by ciliary action 

 through the gill apertures to the atrium, to be expelled through the atriopore. The buccal 

 tentacles, folding over one another, prevent larger objects from entering. Particles small 

 enough to pass through this screen are carried inward to the pharynx, where they become 

 mixed with mucus and are driven against the gill bars. The cilia on the inner faces of the 

 latter, beating in a ventro-dorsal direction, then drive the mingled food and mucus to the 

 dorsal pharyngeal groove, along which it is swept to the oesophagus." Feeding appears to 

 be a continuous process. No doubt the diet includes whatever kinds of microscopic organ- 

 isms may be available at any given time and place. The intestines of the European Bran- 

 chiostoma lanceolatum have been found to contain diatoms chiefly, but also desmids, Fora- 

 minifera. Infusoria, Radiolaria, Cladocera and the eggs of various small invertebrates, 

 as well as plant detritus.* Diatoms have also been reported from the intestines of Lance- 

 lets from Ceylon^ and were again the most abundant item in the diet of young Branchios- 

 toma belcheri at Amoy, China, although the adults also contained the larvae of tunicates, 

 echinoderms and crustaceans.* At another time° this same species in the same general local- 



3. For an excellent photograph of the European Branchiostoma lanceolatum in this situation, see Hagmeier and Hin- 

 richs (Senckenbergiana, 13, 1931 : fig. 3b, 4b, facing p. 258). 



4. Hensen (Ergebn. Plankton-Exped. Humboldt Stiftung, / A, 1892: 24-25) reported the capture of young Lance- 

 lets up to several centimeters long in plankton nets. But the fact that none so large were to be found subsequently 

 in the collections (Goldschmidt, Dtsch. Sud-polar Exped., // Zool. 3, 1909: 235) suggests that the stated size 

 was an error. 



5. Condensed from a detailed account of the feeding mechanism in Branchiostoma lanceolatum, by Orton (J. Mar. 

 biol. Ass. U.K., to [i], 1913 : 19). For an account of the passage of food material through the gut, see Barrington 

 (Philos. Trans., [B] 228, 1937: 271). 



6. For a list of the food of B. lanceolatum compiled from various sources, see Franz (in Grimpe and Wagler, Tier- 

 welt N- u. Ostsee, Lief 7, 12b, 1927: 26). 



7. Tattersall, in Herdman, Rep. Gov't. Ceylon Pearl Oyster Fish., Gulf of Manaar, pt. i, suppl. 6, 1904: 221. 



8. Chin, Philip. J. Sci., 75, 1941 : 393- 9- Reeves, Ginling Coll. Mag. for Jan. 193 1 : 29. 



