68 PHYLUM ENTEROPNEUSTA. 



enteropneust as Balanoglossus or Ptychodera and cannot logically be 

 divorced from the group to which that name is applied. In the second 

 place, Hemichordata is a bad term, because it is not certain that the struc- 

 ture identified as notochord is really such, and because, even if it is a noto- 

 chord, it cannot fairly be said to be " hemi." It might perhaps be termed 

 " probosci," but no one, so far as we know, has suggested this or applied 

 the name Proboscichordata to the phylum. 



Order 1. BALANOQLOSSIDA.* 



Enteropneusta with vermiform, elongated body and many gill- 

 apertures and gonads. 



The Balanoglossida are bilaterally symmetrical vermiform 

 animals, which live in sand or mud in the sea. They have a 

 soft ciliated skin which has the property of secreting mucus, a 

 muscular contractile body wall, and are often highly coloured. 



The body (Fig. 56) is divided into three regions, the proboscis 

 which is the preoral lobe and overhangs the mouth, the collar 

 (kr) and the trunk. The mouth is on the ventral surface at 

 the junction of the proboscis and collar. It is a wide opening 

 and leads into a straight alimentary canal which ends at the 

 hind end of the body in the wide, terminal anus. The hind end 

 of the proboscis (Fig. 56) is narrower than the rest and forms 

 the stalk by which it is attached to the collar region. The anterior 

 end of the collar projects forwards as an annular ridge which 

 completely surrounds this stalk and the mouth. It may there- 

 fore be said that the mouth is directed forward : its dorsal side 

 being formed by the proboscis stalk, and its ventro-lateral walls 

 by .the ventro-lateral portions of the free upstanding edge of the 

 collar (Fig. 60). The posterior part of the collar likewise projects 



* Joh. Miiller, Ueb. d. Larven u. d. Metamorphose der Echinodermen, 

 Th. 2., Akad. d. Wissensch. Berlin, 1849, 1850. A. Kowalevski, Anatomie 

 des Balanoglossus D. Ch., Mem. de I'Acad. imper. des Sc. St. Petersbourg, 

 10, 1866. A. Agassiz, The History of Balanoglossus and Tornaria, Mem. 

 of the American Acad. of Arts and Sciences, 9, 1873. W. Bateson, A Series 

 of Studies in the Anatomy and Development of Balanoglossus in the 

 Q.J.M.S., 24, 25, and 26, 1884-6. J. W. Spengel, Die Enteropneusten, 

 Fauna und Flora des Golfes von Neapel, 18th Monograph, 1893. Id., Die 

 Benennung der Enteropneusten Gattungen, Zool. Jahrb., Syst., 15, 1901, 

 p. 209. Id., Neue Beitrage, etc., ii., iii., iv., Zool. Jahbr., Anat., 20, p. 1, 

 p. 315, p. 413. J. P. Hill, The Enteropneusta of Funafuti, Memoirs Aus- 

 tralian Museum, 3, 1898, pp. 205 and 335. A. Willey, Enteropneusta 

 from the S. Pacific, Witters Zoological Results, pt. 3, 1899, p. 32. R. C. 

 Punnett, The Enteropneusta, Gardiner's Fauna and Geography of the Mai- 

 dive and Laccadive Archipelagoes, vol. ii. pt. 2, 1903, p. 631. E. W. Mac- 

 Bride, Review of Spengel's Monograph on Balanoglossus, Q.J.M.S., 36, 

 1894, p. 385. S. F. Harmer, Hemichordata, in Cambridge Natural History, 

 vol. 7, 1904, p. 3. 



