GEPHYREA. 617 



are, with the exception of two genera, oral tentacles variable in form sur- 

 rounding the mouth, either in a complete or incomplete ring, or aggregated 

 in bundles, which may be entirely dorsal to the mouth. A pair of ciliated 

 tubercles may lie above the supra-oesophageal ganglion. The hind-end 

 of the body is either expanded or pointed and narrow. The Priapulidae 

 are cylindrical in shape, the introvert is short and not slender, and there 

 are no tentacles. The mouth is surrounded by chitinoid teeth, long and 

 curved in Halicryptus. Priapulus has a caudal appendage (double in P. 

 bicaudatus] which is ventral to the anus, hollow, communicating with the 

 coelome, and beset with hollow papillae. The Echiuridae have a long 

 prostomium developed from the larval prostomium, and often termed 

 proboscis, capable of great extension and very mobile, at the base of which 

 the mouth lies ventrally. It is bifid at its apex in Bonellia. The body is 

 cylindrical and tapers posteriorly. There is a pair of ventral chitinoid hooks 

 placed anteriorly in Echiurus, Thalassema, and Bonellia. Echiiirus Pattasii 

 is also provided with two posterior, nearly complete circles of setae ; E. 

 unicinctus with one ; but in some species of the genus the circles in 

 question are wanting altogether. The female Hamingia has no setae. 

 The male in this genus as well as in Bonellia is minute, and Planarian in 

 aspect. 



The integument is composed of a cuticle, a hypodermis, and muscle 

 layers. A layer of connective tissue, or cutis, may underlie the hypodermis, 

 as in Sipunculus and Echiuridae. The cuticle is chitinoid, and sometimes 

 cast off and renewed (Echiurus}. The hypodermis consists of a single 

 layer of cells usually close-set and columnar, sometimes stellate, the in- 

 tervals being occupied by a clear material (Priapulus, Halicryptus}. The 

 colouring-matter of the animal is contained in them. The green hue of 

 Bonellia is due to a peculiar pigment known as Bonellein, which is not 

 identical with chlorophyl as usually stated. It may also be the pigment 

 of the green-coloured Hamingia. Pigment cells are found in clumps in 

 the cutis, &c. The cuticle and hypodermis form together the various 

 processes, papillae, hooks, plates bearing papillae, which occur in different 

 genera. The spines of the Echiuridae are formed in sacs of invaginated 

 hypodermis, those of the posterior circles in Echiurtis from a single cell. 

 Glands are generally present, usually unicellular, sometimes bi- or multi- 

 cellular as in Sipunculus nudus. The musculature of the body consists of 

 an external circular layer followed in Sipuncididae by a layer of oblique 

 and then of longitudinal fibres ; in Priapulidae by a layer of longitudinal 

 fibres alone ; in Echiuridae by a layer of longitudinal and of circular 

 (Greeff) or oblique (Spengel) fibres. The muscles of the different layers 



been said to possess a posterior terminal pore opening into the coelome. There is a depression, but 

 no pore ; and the larva, as figured by Hatschek, has a bundle of sensory hairs at the spot in 

 question. 



