I HEMICHORDATA ENTEROPNEUSTA 5 



logical to regard all Chordata as Vertebrates, since the Inverte- 

 brata are in no sense a natural group with common charac- 

 teristics, their union under one name merely implying that they 

 have no close affinity to the Vertebrates. It is often convenient 

 in practice to divide animals into Vertebrates and Invertebrates, 

 but from a zoological point of view a division of the animal 

 kingdom into Molluscs and Non-Molluscs would have as much 

 or as little significance. 



The sub-phylum Hemichordata l consists of the Orders : (I.) 

 ENTEROPNEUSTA, 2 including Balanoglossus (Fig. 1); (II.) PTERO- 

 BRANCHIA, 3 represented by the genera Cephalodisciis (Fig. 9) and 

 Rhabdopleura (Fig. 12). To these should possibly be added 

 (III.) PHORONIDEA, for the reception of Phoronis (Fig. 13). 



Order I. Enteropneusta. 



Worm-like Hemichordata, with numerous gill-slits, a straight 

 intestine, and a terminal anus. Proboscis separated by a narrow 

 stalk from the simple ring-shaped collar, which is succeeded by an 

 elongated trunk. 



The structure of Balanoglossus, formerly the sole genus 

 belonging to this Order, but now divided 4 into the genera 

 Ptychodera, Balanoglossus, Glossobalanus, Glandiceps, Spengelia, 

 Schizocardium, Harrimania, Dolichoglossus, and' Stereobalanus, 

 has of recent years formed the subject of elaborate investigations 

 by Spengel, 5 Bateson, 6 and Willey. 7 More than thirty species 

 are known, ranging in length from 25 mm. 8 (Pt. bahamensis) to 

 2500 mm. (B. gigas), and for the most part inhabiting shallow 

 water ; Glossobalanus sarniensis occurring between tide-marks in 

 the Channel Islands. Glandiceps talaboti has, however, been 

 dredged near Marseilles from as much as 190 fathoms, while 



1 Bateson, Quart. J. Micr. Sci. xxv. Suppl. 1885, p. 111. 



2 Gegenbaur, Grundziige vergl. Anat. 2 ed. 1870, p. 158. 



3 Lankester, Quart. J. Micr. Sci. xvii. 1877, p. 448 ( = ASPIDOPHORA, Allman, 

 J. Linn. Soc. xiv. 1879, pp. 490 n., 586). 



4 Spengel, Zool. Jahrb. Syst. xv. 1902, p. 209. 



5 Fauna u. Flora G.v. Neapel, 18 Monogr. 1893 (reviewed by MacBride in Quart. 

 J. Micr. Sci. xxxvi. 1894, p. 385) ; Zool. Jahrb. Anat. xviii. Pt. ii. 1903, p. 271. 



6 Quart. J. Micr. Sci. xxiv. 1884, p. 208 ; xxv. Suppl. 1885, p. 81 ; xxvi. 1886, 

 pp. 511, 535. 



7 Zool. Results, Part iii. Cambridge, 1899, p. 223. 8 = 1 inch. 



