IntroducHo7i to Animal Morphology. 207 



The intestine is straight, attached medio-dorsally 

 by a longitudinal band to the body wall, medio-ven- 

 trally by interrupted mesenteric threads, traversing 

 which, close to the ganglion, is a. vessel. The anus is 

 ventral, near the hollow tail, which is divided by a 

 partition, and in which spermatozoa form from proto- 

 plasmic masses detached from its walls, and escape by 

 lateral slits, to which sometimes seminal vesicles are 

 appended. There is a saccular ovary on each side of 

 the intestine, opening beside the anus. An oval, 

 ventral nerve-ganglion (= the cephalic ganglion of 

 Nematodes) sends backwards a pair of lateral branches, 

 and forwards another pair which unite pre-orally in a 

 hexagonal ganglion. This sends off lateral branches 

 to the conical tentacles when they exist (S. cepha- 

 loptera), and two anterior branches to the pair of eyes, 

 which consist of radially arranged crystal cones on a 

 nervous layer and mass of pigment. 



Sometimes a dorsal, wheel-like disc exists, placed 

 like a saddle. The non-ciliated embryos are directly 

 developed, the &^% passing through a gastrula stage. 

 The one genus Sagitta is found in the Mediterranean 

 and Atlantic. Chsetosoma is probably one of its 

 nearest allies. They have been regarded as Verte- 

 brates [Metssiier], or as Molluscs [Forbes). 



Class 10. Enteropneusti {Gege^ihaur) — worm- 

 like, brittle, contractile, dioecious animals, flattened, 

 except at a collar-like swelling in front, and consist- 

 ing of two, lateral, flattened parts, and a middle annu- 

 lated portion showing traces of metameric growth. 

 The finely ciliated, protoplasmic cutis secretes much 

 mucus by its unicellular glands. The muscular coat 

 is strong, the two, lateral, longitudinal bundles of fibres 



