HEMICHORDATA — ENTEROPNEUSTA 



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 af&nity 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.) 

 Entekopneusta,^ including Balanoglossus (Fig. 1); (II.) Pteeo- 

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

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

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



Order I. Enteropneusta. 



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

 intestine, and a terminal anus. Prohoscis separated hy a narroto 

 stalk from the simple ring-shaped collar, ivhich is succeeded ly 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, Han-imania, Dolichoglossus, and Stereolalanus, 

 has of recent years formed the subject of elaborate investigations 

 by Spengel,^ Bateson,'' and Willey.^ More than thirty species 

 are known, ranging in length from 25 mm.'* {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 talahoti has, however, been 

 dredged near Marseilles from as much as 190 fathoms, while 



' Bateson, Quart. J. Miar. Sei. xxt. Suppl. 1885, p. 111. 



'■' Gegenbaur, Gnindzilge vergl. Anat. 2 ed. 1870, p. 158. 



3 Lankester, Quart. J. Micr. Set. xvii. 1877, p. 448 ( = Aspidophoka, AUman, 

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



" 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. Set xxxvi. 1894, p. 385) ; Zool. Jahrb. Anat. xviii. Pt. ii. 1903, p. 271. 



« Quart. J. Micr. Sci. xxiv. 1884, p. 208 ; xxv. Sup:pl. 1885, p. 81 ; xxvi. 1886, 

 pp. 511, 535. 



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



