626 THE ANIMAL KINGDOM. 



The Gephyrea are classified as follows 



1. Gephyrea Achaeta : unisegmental (?) ; fore-part of the body invaginable by 

 means of special retractor muscles ; no setae, at least in the adult ; mouth anterior 

 and terminal. 



(a) Sipunculidae : tentacles usually present at the oral extremity. Nervous 

 system with supra-oesophageal swellings. Alimentary canal spirally coiled as a rule, 

 rarely disposed in loops ; anus dorsal and anterior. Vascular system rarely absent ; 

 closed ; enters tentacles ; blood moved by cilia as well as by one or two contractile 

 vessels. An anterior pair of nephridial sacs, which serve as genital ducts. Genital 

 products set free into coelome, where they mature. Sexes separate (? always). 

 Ova with a zona radiata. Prostomium of larva aborted ; larval setae in Phascolo- 

 soma. Free, or living in shells or tubes, e.g. Phascolosoma, Sipunculus, &c. 



(b) Priapulidae \ introvert short. Nervous system in continuity with hypo- 

 dermis. Pharynx armed with chitinoid teeth. Alimentary canal either straight or 

 slightly looped ; anus terminal. No vascular system nor anterior nephridia. Sexes 

 separate ; genital apertures posterior on either side of the anus ; ducts continuous 

 with the glands. Priapulus with ventral caudal appendage, single or double, beset 

 with papillae ; Halicryptus. 



2. Gephyrea Chaetifera : multisegmental, but segmentation lost in adult. A 

 long extensile prostomium, with the mouth at its base. A pair of ventral anterior 

 setae. Nervous and vascular systems extend into the prostomium. Alimentary 

 canal convoluted ; anus terminal ; a pair of posterior nephridia open into the 

 rectum. One to four pairs of anterior nephridia present, and act as genital ducts. 

 Sexes separate ; genital products set free into the coelome. A minute Planarian- 

 like male in the genera Bonellia and Hamingia. Live in mud or sand, or holes in 

 rock, or shells. 



Echiuridae : Echiurus, Thalassema, Bonellia with bifid prostomium ; Hamingia. 



Gephyrea in general, Danielssen and Keren, Den Norske Nordhavs Expedition, 

 iii. 1881 (cf. A. N. H. (5), vi. 1881, p. 462); lid. Fauna Littoralis Norwegiae, 

 pt. 3, 1877. 



Sipunculidae, Die Sipunculiden, De Mace, Billow, and Selenka, 1884 (with 

 lit.) in Semper's Reisen im Archipel der Philippinen, Part II, iv. pt. i. Golfingia, Ray 

 Lankester, Tr. L. S. (2), ii. pt. 16, 1884 (key to genera). Sipunculus nudus, 

 Andreae, Z. W. Z. xxxvi. 1882 (with lit.); Keferstein, Z. W. Z. xv. 1865; develop- 

 ment of, Hatschek, Arb. Zool. Inst. Wien, v. 1884. Phascolosoma, Keferstein, 

 Z. W. Z. xii. 1862-63, p. 35 ; development of, Selenka, Z. W. Z. xxv. 1875. Aspi- 

 dosiphon, &c., Sluiter, Beitrage, &c., Nat. Tijdschrift. Nederl. Indie, 43, 1883. 

 Segmental and sex organs, Sluiter, Tijdschrift Nederl. Dierk. Vereen. vi. 1882-85. 

 Blood corpuscles and 'Topfchen] Brandt, Me'moires de 1'Acad. Imp. St. Piters- 

 burgh (7), xvi. 1871. Blood-colouring matter, Ray Lankester, P. R. S. xxi. 1873, 

 p. 80; Krukenberg, Vergleich. Physiol. Studien, i. pt. 3, 1880, p. 82. 



Priapulidae, Apel, Z. W. Z. xlii. 1885 ; skin and nervous system, Scharff, Q. J. M. 

 xxv. 1885 ; Ehlers, Z. W. Z. xi. 1861-62 ; Horst, Arch. f. Nederl. Zoologie, Suppl. i. 

 1881. 



Echiuridae: monograph, Rietsch, Recueil Zool. Suisse, iii. 1886; Greeff, Nova 

 Acta, 41, 1879. Echiurus, Spengel, Z. W. Z. xxxiv. 1880 ; development of, Hatschek, 

 Arb. Zool. Inst. Wien, iii. 1881. Thalassema, Ray Lankester, Z. A. iv. 1881 ; 



