CHAPTER XLIX 



LOWER CHORDATES 



The chordates belonging to the first three siibphyla represent three 

 very diverse types. The hemichordates were until quite recently con- 

 sidered worms and the tunicates were formerly put in a phylum by them- 



Proboscis 



Collar 



Mouth 



Pharyngeal 

 Slits 



Fig. 202. — Dolichoglossus kowalevskii (A. Agassiz), found on the Atlantic coast. An 

 adult male. X 2. (From Batesoti, Quart. Jour. Mic. Sci., n. s., vol. 25.) Dolichoglossus is 

 by many considered only a subgenus of Balanoglossus. 



selves and included among the invertebrates. The resemblance of the 

 amphioxus to the vertebrates has, however, long been recognized. 



337. Hemichordata. — The genus Balanoglossus may be taken as a 

 type of this subphylum (Fig. 202). To this genus belong wormlike 

 animals which burrow in muddy areas along the seashore, passing the 

 mud through their bodies and taking out the organic matter in the same 

 fashion as the earthworm takes organic matter from the soil. Different 

 species range in length from an inch to 4 feet, and some of them are 

 brightly colored. The body consists of three portions, an anterior 

 proboscis, a ringlike collar, and a metameric trunk similar in many ways 

 to the body of an annelid. The mouth opening is ventral and just in 



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