I HEMICHORDATA—ENTEROPNEUSTA 5 
logical to regard all Chordata as Vertebrates, simce 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 ' consists of the Orders :—(I.) 
ENTEROPNEUSTA,” including Balanoglossus (Fig. 1); (II.) PrEro- 
BRANCHIA,> represented by the genera Cephalodiscus (Fig. 9) and 
Rhabdopleura (Fig. 12). To these should possibly be added 
(III.) PHoroNIDEA, for the reception of Phoronis (Fig. 13). 
OrderI. 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* 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,’ Bateson,° and Willey.’ More than thirty species 
are known, ranging in leneth from 25 mm.° (Pt. bahamensis) to 
2500 mm. (2. gigas), and for the most part imhabiting 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. Mier. Sci. xxy. Suppl. 1885, p. 111. 
2 Gegenbaur, Grundziige vergl. Anat. 2 ed. 1870, p. 158. 
3 Lankester, Quart. J. Mier. Sci. xvii. 1877, p. 448 (=AspripopHora, 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. 
§ Quart. J. Micr. Sci. xxiv. 1884, p. 208; xxv. Suppl. 1885, p. 81; xxvi. 1886, 
pp: 521, 585. 
7 Zool. Results, Part iii. Cambridge, 1899, p. 223. ao —leimeh: 
