WORMS. 



199 



by special muscles. There are no setce, hence the animals are some- 

 times, but perhaps erroneously, classified as Gephyrea Achaeta. The 

 nervous, system consists of an oesophageal ring, and a median ventral 

 nerve-cord, which shows slight hints of segmentation. There is a 

 spacious body-cavity. 



SiPUNCULID/E. 



PRIAPULID.E. 



The anus is dorsal and anterior, and 

 the food canal is usually in a spiral ; the 

 mouth is surrounded by tentacles. There 

 is a closed vascular system, with branches 

 to the tentacles. 



An anterior pair of nephridia serve also 

 as genital ducts, removing the repro- 

 ductive cells from the body-cavity. The 

 sexes are separate. 



Examples — Sifiitnctihis. 



Phascolosonui. 



The alimentary canal is straight or 

 slightly looped, and the anus is dorsal 

 and posterior. There are no tentacles. 



There is no vascular system. 



No anterior nephridia, but a pair of 

 tubes open beside the anus, and are said 

 to be excretory in the young, genital 

 in the adult. The sexes are separate. 



Examples — Priapulus. 

 HalicrypUts. 



Class Phoronidea. Phoronis. 



This type is represented by one genus, Phoronis, a worm-like marine 

 animal enclosed in a fixed leathery tube. Numbers occur together. 

 The mouth is surrounded by numerous ciliated tentacles. These have a 

 sort of internal skeleton, and are disposed on a horse-shoe-shaped base. 

 The alimentary canal is curved, and ends dorsally near the mouth. The 

 nervous system lies in the ectoderm, and consists of a ring around the 

 mouth, and of a cord down the left side of the body. Two ciliated 

 sensory pits lie beside the anus. The body-cavity is well-developed. 

 There is a closed vascular system with nucleated red cells. Two ciliated 

 nephridia, opening posteriorly, serve also as genital ducts. Phoronis is 

 hermaphrodite. The peculiar larva, known as an Actinotrocha, under- 

 goes metamorphosis. 



Class PoLYZOA or Bryozoa. Sea-Mats, etc. 



Small animals which (with one exception) form colonies. The body 

 is surrounded by a cuticle, which is usually very firm posteriorly. The 

 alimentary canal is curved so that it ends near the mouth. Numerous 

 tentacles surround the mouth, and are often disposed on a horse-shoe- 

 shaped base. The nervous system is represented by a ganglion between 

 mouth and anus. There is no vascular system. If nephridia are present, 

 they are two in number, opening near the mouth, and are not used as 

 genital ducts. All the Polyzoa form buds. The larva is free-swimming. 



