CHAPTER XIII. 



PRIAPULOIDEA.* 



Unsegmented vermiform animals with an anterior terminal mouth 

 and a posterior terminal anus. The central nervous system is not 

 separated from the ectoderm, and the renal and reproductive organs 

 are entirely separate from the body-cavity. 



These are vermiform, animals which live in sand and mud in the 

 sea. They have a short introvert, and the mouth, which is terminal 

 and anterior, is surrounded by chitinous teeth. The anus is terminal 

 and posterior, and in Priapulus there is a hollow caudal appendage 

 attached ventral to the anus, and covered with a number of hollow 

 papillae. There are no tentacles. The body-wall is muscular, and 

 the skin is transversely ridged. 



The alimentary canal is straight, or but slightly looped, and is 

 divided into a muscular pharynx lined with chitinous teeth, an 

 intestine, and a rectum. 



The central nervous system consists of a circumpharyngeal ring 

 and a ventral cord, and is throughout in continuity with the surface 

 ectoderm. 



There are no special sense-organs. 



There is a spacious body-cavity, which is probably a haemocoele, 

 inasmuch as it has no connection with the renal or generative organs. 

 There is no canalicular vascular system, and if the body-cavity be 

 not a haemocoele it must be admitted that the vascular system 

 is absent. 



The renal and reproductive organs are paired, and have common 

 ducts, which open posteriorly, one on either side of the anus. These 

 ducts are beset with two kinds of caecal diverticula the one 

 generative and the other renal. The generative caeca produce the 



* "W. Apel, "Zur Anat. d. Friapulus caudatus u. d. Halicryptus spinulosus," 

 Z. f. w. Z., 42, 1885. E. Ehlers, "Ueb. d. Gattung Priapulus," Z. /. w. Z., 

 11, 1861. H. Schauinsland, " Die Excret. u. Geschlechtsorgane d. Priapuliden," 

 Zool. Anz., 9, 1886. 



