THE ANIMAL KINGDOM 441 



which terminates in an anus at the posterior end of the body. 

 Dorsal and ventral mesenteries support the intestine and divide 

 the coelomic cavity into two pouches. There are dorsal and 

 ventral blood vessels, a portion of the dorsal one being con- 

 tractile. The sexes are separate and there is a metamorphosis 

 in development. Usually a tornaria larva, resembling the 

 larvae of echinoderms, is present. In colonial forms, in addi- 

 tion to sexual reproduction, asexual reproduction by budding 

 also occurs. All are marine. 



*EE3Xi5SpBBSBBBE3S B (I 



y ff M C t 



Fig. 263. — Diagram of the anterior end of Balanoglossus. b, branchial region 

 of alimentary tract with gill clefts; c, collar; d, dorsal blood vessel; dn, dorsal 

 nervous system; m, mouth; n, notochord consisting of a tube of cells connected 

 with the alimentary canal; o, esophagus; p, proboscis; t, trunk; v, ventral blood 

 vessel. 



Examples: Balanoglossus aurantiacus, about 15 cm. long, 

 occurs in sand and mud of shallow water of the Carolina coast. 

 It lacks a tornaria larva. Dolichoglossus kowalevskyi, in the 

 sandflats, Atlantic Coast; Rhabdopleura sp., a deep-sea colonial 

 form without gill slits. 

 SUBPHYLUM 2. TUNICATA. The presence in many 

 tunicates of a mantle cavity, with incurrent and excurrent 

 siphons, gives them a superficial resemblance to molluscs 

 (Fig. 264). The mantle is covered by a tunic composed largely 

 of cellulose. The incurrent opening is the mouth, which leads to 

 the wide pharynx through whose gill slits the water passes 

 either directly to the outside, or into a peribranchial or cloacal 

 space, which opens to the outside by the excurrent syphon. In 

 the mid-ventral line of the pharynx is the endostyle, a glandular 

 ciliated groove, whose cilia move entangled food masses for- 

 ward to the ciliated peripharyngeal band, from which it passes 

 to the dorsal lamina, another ciliate tract in the mid-dorsal 

 line, whence it reaches the esophagus. The latter is followed 

 by a stomach and intestine, the intestine opening into the 

 cloacal cavity. The heart has the peculiar property of period- 



